
VS HDD seems a bit unlikely. The typical cheap optical media isn’t designed or meant for long term archival. There are more expensive types that are meant for long term storage but I’m pretty sure that’s not what OP is talking about, especially if it’s just random blank discs from thrift stores, etc.
But to your point even cheap optical media might outlast SSDs since those tend to lose their saved data if stored unpowered for x years.
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 (?)