The only recent thing I saw was a conversation on reddit with people having the problem, but it was back in the update to 1.10, which is not really that helpful. They also said that logging into the realm as the host updates it and it will update in 72 hours if the host doesn't, yet obviously that is not the case here.
I updated my game, how do you update a realm? I have been having the same issue, and posted about it, yet I have gotten no responses from mods on how to fix it.
How was it not letting you in? Was it crashing your game or just saying you could not connect?
IF YOU USE A TEXTURE PACK THEN TAKE IT OFF AND TRY TO JOIN AGAIN!!!!
With some troubleshooting, I found out my friends who did not play with the texture pack got on just fine, but those who did always crashed. So. with no help from mods, I figured it out after a week of this issue and emailing Mojang trying to figure out how to fix it.
If this works for you, then please tell me, I hope everyone is having the same issue with this problem, and if not, then maybe I can help troubleshoot atleast a little bit