Attached the crash report just now, but maybe a log would be helpful too. I'm not familiar with tech so maybe it's actually useless.
I have the same problem as well. I could connect to the realms server yesterday but crashes when I try to connect today. My crash report:
My friend had this problem yesterday but can connect normally today, probably because of a restart. (Not sure about that as none of us is the owner) My friend's crash report:
this happens at chunk borders for me in 1.13