GtkSpinners stop spinning

At seemingly random moments GtkSpinners stop spinning and reset to their original orientation without rotation.

I have observed this a lot in Pika Backup and also caught it in Software. After porting Pika Backup from GTK 3 to 4 it seems to happen more frequently. In GTK 3 the animation often started again on hovering the spinner. In GTK 4 this does not seem to help, but clicking the spinner can start the animation until it randomly stops again.

I wish I would have more useful debugging information, but I have no idea what else I could track or report.

/cc @exalm