Yeah, I was able to unsubscribe to just 2 or 3 of the most recent ones I subscribed to and this issue disappeared. I'm not going to bother remembering or noting which ones they were. I suspect this is an issue regardless of a specific mission.

Should be easy for the devs to nail this down now that many have reported it has something to do with workshop content. Of course it isn't any single piece of content as more than 1 mission has been reported on this.

Obviously it is something Arma is doing every 10 mins likely in checking if Steam content has been updated or something like that.

Does anyone know if you unsubscribe from everything, is it then fine to re-subscribe?

I have the same issue. This did not happen immediately after the latest stable update but sometime between then and now. I was able to host locally and play just myself MP missions no problem. Then all of a sudden this started showing up this evening.

I tried Vanilla as well with no add ons loaded.

I can reproduce this with a mission downloaded through Steam workshop. I saved multiple times during the game. Then Save&Exit. I don't even quit the game and the save is still not there.