It could be related to this post. There was an issue in one of the libraries we use (Qt) that was fixed by upgrading to a newer version (Qt 5.15.2) for the GPlates 2.3 public release.
However, the user in that post still had problems, and reported that running CCleaner fixed their issue. I think their GPlates could have been using a different Qt5 DLL (than was packaged/installed with GPlates) - and running CCleaner removed that DLL.
Before you run CCleaner, it would be very interesting to know if you get this problem when GPlates is the first application you run after rebooting your computer (so that no other application gets a chance to load a Qt5 DLL before GPlates does) ? That would help confirm whether this was actually the cause.