I've been using a custom theme made by myself based on the focus/card theme since a few months. It's working fine for a client who is on the april 2019 version, but now that I've uploaded it to our own server that has the June 2019 version, it is no longer working correctly.
So what happens? Well, if an app is on the Sense Focus theme and I switch it to the custom theme, it switches for a split second but then returns to a slightly different version of the classis theme layout/CSS wise. The changes in the JSON file do work, but the layout/CSS changes don't. However, if I then press the same custom theme again, the layout works as intended. The issue is that when I publish the app that has the custom theme working (which happens after a 2nd consecutive click on the theme), the published version misses the layout changes again.
The strange thing about this is that it does work when I press the same custom theme two times consecutively. Did anything change in CSS styling? To summarise... it seems that the JSON file does work properly, the issue seems to be with the CSS.