I only have one IMAP account setup and I get perhaps a similar issue. The content of the mailboxes load, but then messages do not load in certain folders. Switching folders back and forth often resolves the issue, all within the same account.

I have multiple IMAP accounts set up. My primary one is my Personal one, with Work mail accounts (3 in total) also present.

Upon startup, I have to switch between two different accounts' mailboxes in order for any mail content to load. Otherwise it will just have an empty textView.

I think it may get confused about the 'selected' mail account at startup. Where while my Personal account is the default, internally not all references may be pointing to it. Which is why switching accounts fixes it.

I have no such issues if I only have 1 mail account active at a time.

Investigating this myself currently and I just want to note it here publicly so others know that it's an issue.