All my work, for at least 3 years, is totally based on MetaBox Suite of Tools. I always updated WordPress to latest versions and everything was always smooth. But this morning I moved to WordPress 5.6 (on a test environment) and, right upon activating my theme, I got severe JS errors, who break the DRAG and DROP functionality and also the TABS on SETTINGS PAGE as well (and I believe it could happen in other instances too).
Need help to start debugging. I have no idea what path should I go since the console logs point to internal WordPress files, and not to my own theme files. Here is the shot:
I know it is impossible to find the problem just by looking this info, but any lead could help. What could I do first?
I will try remove scripts from my theme one by one, perhaps I can find where the whole problem starts, at least.
Any idea, suggestion, comment, could help.
Thank you so much.