I have two realms, one of them opens fine, the other will not open.
It is very difficult to figure out where MCPE Realms support is located, this is the bug tracker and so the link from MC Support on twitter seems a misdirection.
REALMS-123
Can't open Realm "Realm cannot be contacted"
Resolved
Cannot Reproduce
0
Mojang Support can be found at: https://help.mojang.com/customer/portal/emails/new