Have you tried writing to discord technical support? I have heard about such a problem from users of the same iPhone model, so I think that the problem is not specified in your phone. If I were you, I would try downloading the app from
https://applapp.store/en since usually, when there are problems with applications, I try to download them from there, and all the gaps disappear. I do not know what this is related to, but I think it's about the user agreement. If it does not help, you will have to write to the technical support of the application and sort it out with them.