Tried it a few times since yesterday, bot keeps on saying send error until it stops retrying. Other people had the same problem. Actually, seeing the empty history it seems it doesn't work for anyone.

And speaking of history, is there any way to get the histore from before the change back? I'd like to know which items were lost in the meantime and without the history that'll be a major pain.

All the bots have to re-establish their Steam session, and I will do it for you first.

There is no way to get back the history, but I can tell you there is no lost (unless you lost it with trade offer). Because VIP bots are not shared and all the lost items are going to be left in the bot anyway. You only need to check whether the number of items in your inventory matches the number in the bot's Steam inventory.