I often look at the Hot Network Questions list in the various topics that I participate in. The questions are usually interesting (for obvious reasons), so I read them, and the answers, and give up/downvotes all around (including on comments). If I ever upvote a question, I almost always upvote an answer, and vice-versa, assuming that the quality is good. I usually upvote comments that I find useful/interesting/funny as well.
I came back to it today to see if there were any new answers, and to my surprise I saw this:
The thing to note is that the answer wasn't upvoted, though I distinctly remember upvoting it.
This happens infrequently, but often enough that now I'm writing on Meta about it. It seems that sometimes, my votes aren't recorded. This seems to happen most often with Hot Network Questions. I frequent Programmers, Academia and StackOverflow the most, and I often re-read Q/A that I read/upvoted that week, only to come back to find that my votes weren't recorded (when I distinctly remember upvoting those questions and answers).
Has anyone else experienced this? Is this an actual issue or am I being delusional?
In response to comments, I use the web app as well as the iOS app, but more frequently the web app. I'm suspecting that an error occurs during voting, but I happen to navigate away from the Q/A before the error propagates back to me, rendering it essentially 'invisible'. I don't see my answer up-vote for this UX question in my votes tab.