Earlier today, a tranche of upvotes was removed from select sites once it became clear enough (given the available evidence) that they were cast with little-to-no consideration for the content of the posts. Further specific information about this case will stay limited to the moderators of the affected sites and the user(s) directly involved.
Just to clarify, vote reversals do not typically mean you've done anything wrong - but I can confirm that's true in this case. You've done nothing to worry about. This vote invalidation affected a decent number of people, and you unfortunately happened to be one of them.
While we have the ability to remove significant parts of the voting record, it's not a joyous experience for anyone. This type of vote invalidation is uncommon, and isn't done lightly. We weigh both the volume of users affected, and whether the invalidation is as small as we can reasonably make it. (We also routinely consider our confidence in the evidence we have.)
While I can't take questions specific to this case, I'm still happy to clarify questions about general policy - at least, when I'm confident in the answer!