I have just updated Ren'py to 8.1.1 (from 8.0.1 previously) and I have run into graphical glitches that didn't use to happen before, not changing any of the code.
First, when first opening the game, sometimes all buttons on the first screen shown have a black mark where the text should be. Hovering with the mouse over the buttons removes the black marks, and they don't come back until a later restart (I doesn't happen on every restart either, and sometimes not even on every button).
Going to the console, I see a bunch of new 'Leaking texture' messages show up, which I assume are related:
Second, I use a version of the ProportionalScale class to resize pictures at init. Similarly, the first background picture displayed after starting the game (summoned with 'show') is not actually resized, but all other pictures shown afterwards seem to resize normally. While the first does not show at the right size, going full screen then back to window mode solves the problem and the picture is then shown proportionally.
I never had these glitches before so I don't really know where to start to fix them. It never happened previously in 8.0.1 (in fact I have it still installed, and going back to that version everything works fine).
The game uses an edited version of a legacy theme (crayon), if that means anything.