I just saw something that stood out for me when I looked at your code...
Normally, for
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, you name the files "side <character> <attribute>.jpg, png, webp" etc... Yours, however, are named backwards, and with an underscore. So "eva_side.webp" as an example. That might be confusing Ren'py, as it tries to make a pool of side images to choose from, based on your character declarations.
Another possibility is that maybe you changed the file types between an earlier version and this one? I don't have your older versions still on my computer so i can't check, but if your first versions were png's, for example, and you changed them to webp's, which are what this version has, then the save files could be causing issues. You'd have to delete the persistent data like DeUglyOne did above.
Another issue I see is that your side images are a mixture of lower case and upper case first letters, while all your character image declarations are uppercase.
Off topic.. I laughed when I went to the trouble of downloading and putting UnRen in your game folder, only to realize you didn't archive it, haha