Check the log file & see if there's any additional information you can troubleshoot with. According to your .conf it's in /var/log/samba/log.%m
And/or maybe increase the logging level and hopefully when the issue re-occurs you'll have lots more log info to work with. (may have to be careful with the log file sizes though) Not sure if you need to enable client specific logging or maybe just working with the main smb.conf file is enough, see the wiki
https://wiki.samba.org/index.php/Client_specific_logging
EDIT: If you're not already seeing any logs maybe you do need to try enabling client specific logging (?)
Voting for the proposal, would be nice to opt out of extra tracking beyond what already gets tracked/logged during typical Lemmy usage.
But in the grand scheme of things this is more of a Lemmy network problem, if that site exists then surely other sites/tools exist (or will soon) to do the same thing. I've always kind of figured it doesn't take much to start up a Lemmy instance, federate with others, & just start logging the info being sent across the instances (in this case upvotes/downvotes).
You've kind of got me wondering how Piefed handles that but that's another topic really.