Whenever I try to upvote a comment, I get this warning and the upvote does not take effect.
When I try to upvote a post, I don’t get a warning but the upvote also does not appear.
This happens both on the web interface (Firefox with extensions, also tried in stock Firefox and got the same result) and in the mobile app I use (Thunder).
AFAIK it started maybe three weeks ago? Not 100% sure cause I was off Lemmy for a bit of time.
A quick startpage search yielded no useful result…
Any idea on what could be causing this behaviour?
Let me know if I need to provide more information for troubleshooting.

Come on, you can do better.
On the wikipedia page you linked, there is exactly zero occurrence of the word “pain”.
The only part that could remotely be linked to your previous argument does not indicate pain at all.
This paragraph is a less sensational and more serious reformulation of the source material, an opinion piece stating the following without a single scientific reference
This piece was posted in May 2012 on mentalfloss.com, so not really a scientific study.
Also, nothing in there speaks of the brocoli, which you first referred to.
Edit: spelling, formatting