I had this situation too, tapping the theme button did nothing although personalisation_app (sudo) still worked.

None of the suggestions in the thread worked but I found my solution: press the "restore original settings" and typed in the code 12345, after rebooting the theme button worked again. So another 2 hours of restoring my setting but at least I didn't have to reflash which will waste 5 hours.

Possible causes of the problem: maybe installing new kernel, CSSU updates, dunno. Haven't added any new themes, widgets or icons since last reflash.