Markdown preview intermittently blank (just a white page)

You mean the message preview in the main window?

Is it triggered by a particular type of email (large, HTML, ...)? What happens if you select a few other emails and go back to the “buggy” one?

Do headers display in the message view?

Does it appear to only happen in widescreen mode?

You mean the message preview in the main window?

CORRECT.

Is it triggered by a particular type of email (large, HTML, ...)?

HTML emails. However, when triggered, it then affects all emails.

What happens if you select a few other emails and go back to the “buggy” one?

Sometimes it recovers, sometimes it requires a reboot.

Do headers display in the message view?

Yes the do.

does it appear to only happen in widescreen mode?

Mostly yes, I have seen it in three pane view occasionally.

By “reboot” you mean relaunch, right?

The fact that it affects all subsequent emails is interesting. This indicates some kind of deadlock which might require something to time out before it then works again (if not relaunching). Therefore, I suspect it's related to running an external script.

Could you try launching from a Terminal window and then see if there is any output when this happens:

/Applications/MailMate.app/Contents/MacOS/MailMate

Also, I note that you write that multiple relaunches are some times needed (in your original description). Do you think the issue might be triggered by specific emails?

Does resizing the window make any difference (this triggers some re-layouting of the message view)?

Using 5820 and haven't observed this behaviour again. I completely uninstalled MM so this might've been a factor to fix it, but I am not sure.

I think close this ticket.