gsutil: gsutil rsync doesn't recognize some directories as suitable for transfer

While trying to move directories recursively to GCS, I’ve run into this error on almost every directory:

CommandException: arg (./guix-backup) does not name a directory, bucket, or bucket subdir.

I’m guessing the tool detects these as files instead of directories for some reason. Here’s output from two commands. One that works and one that doesn’t.

build-staging ~ # ls -lsa /var/log
total 244
  8 drwxr-xr-x.  4 root root              4096 Jun 13 08:49 .
  8 drwxr-xr-x. 11 root root              4096 Aug  2 16:48 ..
  4 -rw-------.  1 root utmp                 0 Jun 13 08:49 btmp
  4 -rw-r--r--.  1 root root                 0 Jun 13 08:49 faillog
  8 drwxr-sr-x.  4 root systemd-journal   4096 Jun 13 08:49 journal
  8 -rw-r--r--.  1 root root            146292 Aug 10 18:46 lastlog
  8 drwx------.  2 root root              4096 Jun  7 23:19 sssd
196 -rw-rw-r--.  1 root utmp            190080 Aug 10 18:46 wtmp
build-staging ~ #  gsutil rsync -r /var/log gs://guix/logs
Building synchronization state...
Starting synchronization
build-staging ~ # ls -lsa /gnu
total 2884
   8 drwxr-xr-x.    5 root root      4096 Aug  2 16:09 .
   4 drwxr-xr-x.   19 root root      4096 Jul 12 08:50 ..
   0 drwxrwxr-t. 1304 root hamann       0 Aug  9 21:44 store
 488 drwxrwxr-t. 1053 root hamann  491520 Aug  2 14:25 store-old
2384 drwxr-xr-x.   35 root root   2433024 Jul 31 18:28 store2
build-staging ~ #  gsutil rsync -r /gnu/store2 gs://guix/store-test
CommandException: arg (/gnu/store2) does not name a directory, bucket, or bucket subdir.