ah, I checked github now. I see Holger fixed it, and I see it was only reproducable on a newly created Comments.

The problem I've seen is completely random. Could be 1 in a 1000 upvotes that just silently fails. Actually the .upvote method returns a valid vote, so no error, but it is not added to the blockchain. Few users talked about it on Discord.
It doesn't necessarily need to be linked to Beem, but I had users complaining just after switching to beem. Need some more time to try to debug that one... :)