Themify Builder Lite was doing the same after the last update – couldn’t edit anything already published, which rendered it unusable. Have ditched it and redoing all my pages, with Elementor page builder, infintely better, and a more professional look.
Changing Accessibility mode did fix my issue with Themify, and I just checked, it is still working OK, and can be edited.
I received no support from themify over the Builder Litre issue, maybe they just want you to buy the Pro version??