Do you have any idea on what caused it?

https://news.social-protocols.org/stats?id=48104663

This seems to have gone to -10 and then went up according to this, which matches what your comment had said that you were seeing -10 on your android.

Edit: (actually it had gone all the way to -15) and seems that this website has been still stuck at -8 upvotes at the moment of this comment and this link has also been the proof for me to finally see/confirm this as the submission now has positive upvotes.

It is hardly a satisfying answer, but I haven't the foggiest what caused it. I submitted it the same as I've submitted many other submissions in the past.