Error while processing Streaming History JSON

Dear stats fm team!

I have encountered an error while trying to upload and import my extended listening history. I have 8 JSON files in my ZIP file received from Spotify, and when I try to import it in stats fm, 2 of those, the files containing my 2018-2020 streams, return with "failed", and an error message. I have no idea why this could be, since I opened them with a text editor and they work/look just fine, like the other ones. I tried removing all imports from the app and reimporting, and it didn't work. I even separated the files in another ZIP and tried uploading them separately, still no success. This is really annoying because if I paid for your app, I want to be able to use it to its fullest, and that's not the case if I lose 2 years of listening because of a bug. Can you help me resolve this issue, and/or look into what could cause this?

Thanks for further help.