One of the guilds I am in switched away from Vanilla forums for precisely these types of reasons - their products have just not been reliable. Where the guild differs from whatever the official UO forums are doing is that we were able to successfully migrate to new software instead of sticking with the frustrating Vanilla situation - with fifteen years worth of data none-the-less. If a guild can do it with people who are unpaid and doing it for the love of the game, I don't see why the official folks are unable to come up with an alternative solution. It's made the forums virtually unusable for a large majority of players who aren't going to download Firefox just to use one specific website. It's a real shame that this is the predicament we've been forced to deal with.
Admittedly, it's easier said than done to simply 'migrate to a new forum' and I won't pretend like it's something that can be done with the click of a button or zero financial implication, but you'd think after more than a year of this non-sense there would atleast be some more meaningful communication as to what their plans are. It's not like there are 100,000+ threads to move. Even if they just locked the current forums for posterity and moved to a new format - something - anything would be better than current situation.
That said, I have Firefox on my phone and only use it on the rare occasion I have to log into contact someone through main forum - or to post on a topic related to publish releases since Kyronix will be more responsive there. That's about the only way to reliably use the forum without getting logged out in the middle of a post.