Problem with B-Team

The problem I've been having with Attack of the b-team servers is when I try to login to the aternos server I made for the mod pack, it states I'm logging in, but then the screen changes to downloading terrain and gets stuck on that. After a minute an internal server error occurs and when I look at the aternos website it says the server is running and someone is on it, even though I wasn't able to log in. After that, I tried to rejoin but the server said "Can't Reach Server" even though the website states the server is still online. Please help and thanks :D.

Its the same version and everything. I tried restarting it but the same thing happens. I havent been able to play for weeks now because of it.