Any specific logs I can inspect?
I'm not very familiar with FreeNAS (since it's based on FreeBSD), but i would check directory
/var/log and check
syslog file.
cd /var/log
cat syslog | grep electrs
Sorry, but this is a question for the author to analyze his problem. I think there is a problem with the mempool
Why do you think the problem is related with Bitcoin Core's mempool?