Strange error on the CI Windows server

Hello!

I use the AppVeyor CI service to test the application in Windows.
Sometimes tests fall with the following message:

wxTextMeasure::BeginMeasuring(): Must not be used with non-native wxDCs

This error appears either in all tests with the GUI, or in none of
them. Restarting tests helps with a 50% probability. Locally I have
never encountered such a error.

Support for AppVeyor for a long time, but I could not find the reason.
Maybe there are ideas, because of what can such an error appear?

Python 3.6, wxPython 4.0.3.

ยทยทยท

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Best wishes.
Eugene Ilin
http://jenyay.net