plasmach,
Sorry that you are seeing this issue. I assume you are working with the latest CodeMix CI 2020.4.7. If no, then please go to Help > Check for Updates and update to the latest release.
1. Can you please elaborate more about the issue? Which exact file associations are you seeing being reset on Eclipse restart? Also share the before and after restart file editor association details.
2. Do you see the issue in a fresh new workspace as well?
3. Please share with us the Eclipse version details along with .log file located in the workspace dir/.metadata/.log (change the extension to .txt and attach it here) for further investigation.
Apologies for inconvenience caused.
–Swapna
Genuitec Support