I can access private messages OK on my Windows laptop. However, on my Android phone when I go in to private messages I see the start of the message but when I click on it to read the whole message I get the Error 500 message. I.e., "our server is having a moment and we are making it a strong cup of tea!"
It must be a long cup of tea because this has been going on for at least a week. I have Android version 9 on a Huawei phone.