Ubuntu 20.04.2 LTS. I've got the following problems using the "Screenlet" widget in GMB 1.1.99 Beta:
1. Transport buttons do not always display on mouse over. They work once on an initial mouse over and then on next mouse over they don't appear. After waiting a long time, (doing something else on computer) they will reappear on mouse over.
2. Intermittently, when restarting GMB, the size of the Screenlet widget will automatically enlarge itself even though the settings for the Screenlet widget image size have not changed. Attempting to change the settings from within GMB won't work to restore the correct size. The only way I found to correct this is to delete the current "GMB" config file and rename the previous days "GMBxxxxx.bak" file to "GMB". Restarting GMB then restores the Screenlet widget to the correct size.
3. Very long song titles are not well centered. a long song title is cut off on the left side. Mousing over the song title fails to slide the long title so that you can see it all, particularly the beginning left side (as it did in previous versions).
4. Forgot to add. Left clicking on "Screenlet" to pop up track list and then selecting a specific track to play, also doesn't work. In earlier versions of GMB this worked.
I hope a newer, improved version of the GTK3 version appears soon.