I upgraded to this version, 1.2.29, from version 1.2.28, and it obliterated all styling. None of the CSS or themes worked properly after the upgrade. It looked like 1990s era web site, and was so unusable I was forced to downgrade again. I went through the usual upgrade process I’ve followed for the last dozen upgrades I’ve done, so I’m not sure what’s going on.
I suspect the themes support changes might conflict with Customizer or something along those lines. Anyway, caveat emptor to anyone considering upgrading–make sure you have a downgrade path.
Updated Customizer, it will work functionally, now. That said, none of the themes take the new Dark Mode into account, so if combining a Customizer theme with Dark Mode, you might not like the results.
given time, i might integrate it better with freds new theme model, and provide more fluidity between the 2, as well as add both light and dark versions of each theme within Customizer.
On a side note, if you use with “Application Branding” plugin by aljawiad with Customizer, it will revert to previous layout and not work with 1.2.29, until he updates.