That error usually means that the Jobe server is misconfigured or simply down. You say a reboot fixed the issue but the error then returned. That suggests that Jobe is actually failing for some reason. [I assume you rebooted Jobe, not the Moodle server?] Perhaps out of disk space or inodes? Jobe's disk requirements don't usually grow significantly over time unless question authors upload a vast number of questions with support files. But it might pay to look in /home/jobe/runs - if debugging is enabled and has been for a long time, that directory will be full and you could run out of disk space over time.
I suggest:
- When logged into jobe, use the df and df -i commands to check disk space.
- With the firewall down, point the browser at http://<jobehost>/jobe/index.php/restapi/languages. What you should get is a JSON-encoded list of languages.
- Log into Jobe, cd'ing to /var/www/html/jobe and run the tester:
python3 testsubmit.py
That should tell you if Jobe is working correctly.
If none of those point the finger anywhere, work through the Debugging checklist at https://github.com/trampgeek/jobe/blob/master/README.md
Richard