That is odd, normally you are only asked for a reason when you sign up for a new account and not when you just subscribe to a community. Can you share the community you were trying to subscribe?

I have to wait to be subscribed to the different communities That is unfortunately in the nature of the decentralization. Your instance cannot be sure that that the instance the community is on will respond in a timely fashion so it shows it as "pending". The only thing we could maybe do about this is to be overly optimistic. Most requests to subscribe a community go though without a problem so we could just show it being subscribed even though are are not, but that would introduce other problems.