It seems this is broken on most/all platforms and has been this way for a significant amount of time. I personally am seeing the issue on the latest iOS release. As we are all paying for this unusable feature, I am curious if someone from Mojang might weigh in on what is causing the error(s) and when a resolution is expected. All I have heard so far is that they are working on it; however, that does not mean we will see a fix in the near future. Would it be best to cancel the subscription until this is resolved?
Following the steps from Michael's comment I am no longer able to either re-open my realm or reset my world in addition to the main issue; being unable to replace my world. Sadly, realms is complete broken for me now. I have created REALMS-4710 to track those issues as well.