After some hours searching and testing and reviewing the logs the solution was much much easier and provide it here to save some people from headaches
If after an upgrade or migration you are unable to use user panel and getting the HTTP 500 error then follow the next steps to fix the issue.
1. Login to your panel
2. Select User Accounts --> Features,Themes,Languages
3. Select everything to the tab "Themes"
4. Hit the button "Save Theme Default"
5. Change if again to your theme or just leave it as it is
6. Enjoy the magic and do not forget to leave a thumb up as no script was used finally!
Αν το παραπάνω άρθρο σας φάνηκε χρήσιμο θα το εκτιμούσαμε αν μας αξιολογούσατε κάνοντας κλικ εδώ --> g.page/r/CeAOj46Cf2epEB0/review
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