Spotty Last.fm scrobbling

Not sure if this is the right forum, apologies in advance.

I use Plexamp (on iOS) to play music from PMS on Synology NAS (DSM 7.0-41890). Last.fm integration is set up (and I refreshed it recently) but the system doesn’t scrobble reliably. It literally works one day and stops the next.

I’m not sure how to debug it, would appreciate some guidance.

The scrobbling completely stopped on my Windows 10 server on the 15th.