I wonder if this is a common experience?
Well, "this" is broad, but I expect that failing to notice enmity, and relatedly being unaware of consequent social attacks, is a pretty common experience, especially in "polite" social contexts (that is, ones in which overt expressions of conflict violate social norms).
"Crocker's Rules" are an attempt to subvert this; you might find it useful to declare that you operate under them... though I would expect not... in cases like you describe I expect that the downvoter(s) will not wish to be identified.
I wish you luck in deciphering the reason(s).
As someone with no particular aptitude in general niceties, I always welcome Crocker's rules, and mistakenly assume that others do, too.
I wish you luck in deciphering the reason(s).
My best (but still low-confidence) guess, based on the timing and on being overly critical in a comment is that this may have been taken as overly harsh.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.