Hi!
When does it occure? Please share more info, so we could pass this to our programmer, thanks!
Did you use an old save or did you do a fresh start? Can you by any chance share your save file (Upload it on mega or some other cloud service), so we could take a closer look at it.
Cipheos (our programmer) also asks if you could write what exactly you did when you started (if you started a new game without a save) — like where you went or what you clicked.
We're sorry for asking all this stuff, but it would really help us to identify the issue, so thank you in advance if you decide to help us!
I got a similar exception! I had no older saves (they were manually deleted), and can reproduce the error rather reliably:
From some quick websearch it seems that Ren’Py is trying to remove an element that doesn’t exist yet. If that’s correct odds are that this bug only triggers at the start.