iphone: emails sorted into icloud folders are completely blank
i have icloud configured so that email messages from specific senders are sorted into folders. when i receive an email from those senders, it shows in the list of messages in that folder. however, when i try to open that message in the mail app on my iphone, i get a blank, white screen. no text. going back to the message list in the folder shows the message as unread.
if i try forwarding or replying to the message, the typical forward/reply screen appears and i can see the text of the email to which i am replying (but i cannot click any links in the message). if i try to move the message to my inbox, the mail app crashes.
this behavior is 100% repeatable, regardless of whether i reboot the iphone, close and reopen the mail app, or do anything else. messages that are not sorted into folders behave normally.
iPhone SE, iOS 12