Yepp, so my newest and final results: This is completely redonkulous. There is literally no rule to when there is an error or not. It happens always at the same moments, but yet still somehow no pattern.
So I was replying to a message and updating the text by one additional word at a time to see when and what would cause an error. ...I got 3 words, and it would always bug out at that exact same position.
I just tried to put in a copy of that text here, but yes, it results in the above error, so here it is as picture:
If I wrote "from", error. If not, fine. There is no special sign, no function, style, or sign count. It just doesn't like this word. It is not that the word gets blacklisted though, nope. From from from. You can write that. Just in this constellation, it somehow causes an error after only 277 signs. If I write another word than "from" in the text above however, it works.
So, yes, redonkulous, and completely nonsensical.