Losing settings after update

This theme has a lot of potential if it could only work consistently.

Hours after I installed it an update was made available which made me lose ALL customization, it reverted to the demo site which is very frustrating and it never happened with other theme updates.

Also, every time I click “Save & Publish” from any section of the customizer I get this error, even though I haven’t checked anything in that section or even tried to access the Advanced Options.

Please help, I am trying to get this website ready to go live but I am afraid to waste time if it’s going to revert back to demo again.