Unknown devices needs service restart

Hello!
I'm using traccar 5.8.
I had two incidents within 2 weeks apart where the number of unknown devices increase fast and dont recover themselves, it needs a traccar restart command to put them in online/offline states again
No error or warnings in tracker-server.log
Where/how do I start troubleshooting?

These are the things I would check:

1. Process status, like memory, number of threads and connections etc
2. Number and status of database connections
3. Get thread stack traces using jstack tool or something similar to see what is stuck

Hi Anton, thanks for the answer
I have 125 devices currently. free -m command reports the following: total 6144; used: 1142; free:47; buff/cache:5054; available: 5096. What do you think?

I think you missed other points I mentioned.