pagermon: Pushover causing application crash

Noticed this in my logs tonight - Seems to be causing the app to crash and restart, however the notification is sent.

May be benign but not sure.

2|pagermon |     at IncomingMessage.<anonymous> (/home/user/pagermon/server/node_modules/pushover-notifications/lib/pushover.js:167:12)
2|pagermon |     at emitNone (events.js:111:20)
2|pagermon |     at IncomingMessage.emit (events.js:208:7)
2|pagermon |     at endReadableNT (_stream_readable.js:1064:12)
2|pagermon |     at _combinedTickCallback (internal/process/next_tick.js:138:11)
2|pagermon |     at process._tickDomainCallback (internal/process/next_tick.js:218:9)
2|pagermon | 2018-09-18 06:45 +00:00: (node:3588) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 echo listeners added. Use emitter.setMaxListeners() to increase limit
2|pagermon | Error: user identifier is not a valid user, group, or subscribed user key
2|pagermon |     at Pushover.errors (/home/user/pagermon/server/node_modules/pushover-notifications/lib/pushover.js:84:13)
2|pagermon |     at IncomingMessage.<anonymous> (/home/user/pagermon/server/node_modules/pushover-notifications/lib/pushover.js:167:12)
2|pagermon |     at emitNone (events.js:111:20)
2|pagermon |     at IncomingMessage.emit (events.js:208:7)
2|pagermon |     at endReadableNT (_stream_readable.js:1064:12)
2|pagermon |     at _combinedTickCallback (internal/process/next_tick.js:138:11)
2|pagermon |     at process._tickDomainCallback (internal/process/next_tick.js:218:9)