I have found a solution to the problem with the wrong fonts. In case anyone has the same problem at some point, this is how I was able to fix it:
With the plugin “Use Any Font – Custom Font Uploader” I uploaded the fonts again and now they are displayed correctly.
Don’t get me wrong, the problem with the wrong fonts existed even before the last update.
The small text only appears since the last update.
Thanks for the quick reply!