I don't know for sure what was happening during the updates, but if you had 80MB worth of hotpot attempts then I think the update was progressing on the server, but was taking some time because of the volume of data.
Anyway, it seems that the data about attempts was not important to you, in which case emptying the "hotpot_events" table was the best way to go.
> What causes this to happen?
I'm afraid I don't know the answer to that question. The upgrade is supposed to be smooth and hassle free.
It looks like you have upgraded now and are moving on, but I would still welcome the opportunity to have a look at your hotpot tables to check things are as they should be.
all the best