php-fpm_exporter: Error scraping PHP-FPM: invalid character 'c' after object key:value pair

From time to time, and usually two times in a row, we get the following error:

time="2018-05-23T04:52:38+02:00" level=debug msg="Pool[unix:///dev/shm/.php-fpm-www.socket;/php-fpm-www_status]: {\"pool\":\"www\",\"process manager\":\"dynamic\",\"start time\":1524128546,\"start since\":2915412,\"accepted conn\":609721,\"listen queue\":0,\"max listen queue\":0,\"listen queue len\":0,\"idle processes\":17,\"active processes\":2,\"total processes\":19,\"max active processes\":17,\"max children reached\":0,\"slow requests\":6, \"processes\":[{\"pid\":3915,\"state\":\"Idle\",\"start time\":1527039619,\"start since\":4339,\"requests\":314,\"request duration\":37475,\"request method\":\"GET\",\"request uri\":\"/vbseo.php\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":80.05,\"last request memory\":6291456},{\"pid\":3872,\"state\":\"Idle\",\"start time\":1527039607,\"start since\":4351,\"requests\":315,\"request duration\":30692,\"request method\":\"GET\",\"request uri\":\"/showthread.php?t=56371&page=14&p=525978\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":65.16,\"last request memory\":6291456},{\"pid\":2712,\"state\":\"Idle\",\"start time\":1527039447,\"start since\":4511,\"requests\":325,\"request duration\":75745,\"request method\":\"GET\",\"request uri\":\"/vbseo.php\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":79.21,\"last request memory\":8388608},{\"pid\":786,\"state\":\"Idle\",\"start time\":1527039189,\"start since\":4769,\"requests\":341,\"request duration\":61293,\"request method\":\"GET\",\"request uri\":\"/member.php?tab=activitystream&type=user&u=48390\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":81.58,\"last request memory\":8388608},{\"pid\":3471,\"state\":\"Idle\",\"start time\":1527039557,\"start since\":4401,\"requests\":319,\"request duration\":24029,\"request method\":\"GET\",\"request uri\":\"/css.php?userid=109621&cssuid=0&d=1526688000&td=ltr&styleid=0&sheet=userprofile.css\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":83.23,\"last request memory\":5505024},{\"pid\":5560,\"state\":\"Idle\",\"start time\":1527039843,\"start since\":4115,\"requests\":299,\"request duration\":145588,\"request method\":\"GET\",\"request uri\":\"/index.php\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":75.56,\"last request memory\":9437184},{\"pid\":14203,\"state\":\"Idle\",\"start time\":1527022056,\"start since\":21902,\"requests\":1852,\"request duration\":223628,\"request method\":\"GET\",\"request uri\":\"/vbseo.php?pp=40\\\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":40.25,\"last request memory\":7602176},{\"pid\":13435,\"state\":\"Idle\",\"start time\":1527036435,\"start since\":7523,\"requests\":574,\"request duration\":25887,\"request method\":\"GET\",\"request uri\":\"/attachment.php?attachmentid=92642\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":77.26,\"last request memory\":5242880},{\"pid\":16724,\"state\":\"Idle\",\"start time\":1527036888,\"start since\":7070,\"requests\":534,\"request duration\":24909,\"request method\":\"GET\",\"request uri\":\"/css.php?userid=57961&cssuid=0&d=1525436596&td=ltr&styleid=0&sheet=userprofile.css\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":80.29,\"last request memory\":5505024},{\"pid\":20246,\"state\":\"Idle\",\"start time\":1527037377,\"start since\":6581,\"requests\":483,\"request duration\":81230,\"request method\":\"GET\",\"request uri\":\"/css.php?styleid=7&langid=1&d=1498640725&td=ltr&sheet=activitystream.css,sidebar.css,forumbits.css,postbit.css,postbit-lite.css,showthread.css,member.css,user,57961\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":36.93,\"last request memory\":5767168},{\"pid\":11343,\"state\":\"Running\",\"start time\":1527026174,\"start since\":17784,\"requests\":1358,\"request duration\":131,\"request method\":\"GET\",\"request uri\":\"/php-fpm-www_status?json&full\",\"content length\":0,\"user\":\"-\",\"script\":\"-\",\"last request cpu\":0.00,\"last request memory\":0},{\"pid\":1124,\"state\":\"Idle\",\"start time\":1527043730,\"start since\":228,\"requests\":17,\"request duration\":288,\"request method\":\"GET\",\"request uri\":\"/php-fpm-www_status?json&full\",\"content length\":0,\"user\":\"-\",\"script\":\"-\",\"last request cpu\":0.00,\"last request memory\":262144},{\"pid\":1555,\"state\":\"Running\",\"start time\":1527029298,\"start since\":14660,\"requests\":1071,\"request duration\":76318,\"request method\":\"GET\",\"request uri\":\"/vbseo.php\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":0.00,\"last request memory\":0},{\"pid\":21234,\"state\":\"Idle\",\"start time\":1527027536,\"start since\":16422,\"requests\":1226,\"request duration\":106054,\"request method\":\"GET\",\"request uri\":\"/index.php\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":84.86,\"last request memory\":8388608},{\"pid\":2496,\"state\":\"Idle\",\"start time\":1527024938,\"start since\":19020,\"requests\":1516,\"request duration\":28053,\"request method\":\"GET\",\"request uri\":\"/css.php?styleid=7&langid=1&d=1498640725&td=ltr&sheet=activitystream.css,sidebar.css,forumbits.css,postbit.css,postbit-lite.css,showthread.css,member.css,user,109621\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":71.29,\"last request memory\":6029312},{\"pid\":1803,\"state\":\"Idle\",\"start time\":1527024845,\"start since\":19113,\"requests\":1523,\"request duration\":87234,\"request method\":\"GET\",\"request uri\":\"/vbseo.php\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":91.71,\"last request memory\":7340032},{\"pid\":28318,\"state\":\"Idle\",\"start time\":1527038495,\"start since\":5463,\"requests\":394,\"request duration\":328685,\"request method\":\"GET\",\"request uri\":\"/vbseo.php\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":57.81,\"last request memory\":12582912},{\"pid\":15603,\"state\":\"Idle\",\"start time\":1527022259,\"start since\":21699,\"requests\":1830,\"request duration\":106650,\"request method\":\"GET\",\"request uri\":\"/member.php?u=58736&tab=likes_received\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":56.26,\"last request memory\":8388608},{\"pid\":6557,\"state\":\"Idle\",\"start time\":1527025507,\"start since\":18451,\"requests\":1430,\"request duration\":65876,\"request method\":\"GET\",\"request uri\":\"/member.php?u=28953&tab=aboutme\",\"content length\":0,\"user\":\"-\",\"script\":\"/www/myforum.com/vbseo.php\",\"last request cpu\":91.08,\"last request memory\":8388608}]}"
time="2018-05-23T04:52:38+02:00" level=error msg="invalid character 'c' after object key:value pair"
time="2018-05-23T04:52:38+02:00" level=debug msg="Updated 1 pool(s) in 1.965012ms"
time="2018-05-23T04:52:38+02:00" level=error msg="Error scraping PHP-FPM: invalid character 'c' after object key:value pair"

And a few times we got this error (we don’t have the full debug line, because debug wasn’t enabled then):

time="2018-05-21T13:21:39+02:00" level=error msg="Error scraping PHP-FPM: invalid character '%' after object key:value pair"

Looking at the json, I would say that it is correct, so I have no idea what could be the issue.