I have a similar problem :
whenever I try to adjust my character's position using right click in combat, I lose the cursor (and can't adjust the character's position, can't make it turn) and can only get it back with a /reload
-# I want to make clear : I don't have any issue when out of combat, it's only as soon as the combat start I can't right click anymore or I risk losing my cursor until the next reload
I've pinpoint WeakAuras as the culprit (or at least some kind of interaction between something and weakaura) because I tried disabling my addons and it was the only one that made a difference (didn't have the issue with the addon disable, but as soon as I enable it again, I start having the issue)
It only started occurring today after I did the update (I'm on EU server)
Also, I don't know why, but the game still flags the addon as out of date even though I'm on the latest version (5.19.3)
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EDIT TO ADD
I use a similar weakauras as the one in the original message
-# MouselookStop
to disable right clicking in combat and avoid switching target accidentally
I tried disabling it and my issue disappeared
I think we're on the right track and it does indeed have something to do with weakauras designed to prevent right clicking in combat 