Playback monitor randomly letterboxes output

[Paul_WTVT]

I'm using 25.5.0 on a Macbook Pro running 15.7.2 through a dock with 2 external monitors, using the left for editing and right for playback... however I have an intermittent issue when adjusting elements on the timeline during playback, the playback monitor will letterbox the output and the overlays from the program panel will appear... I have to click into a different timeline and back for it to resolve... I can't work out how to prevent it or fix it??? 

(attached is the same frame with/ without the error as seen on the playback monitor)

[hashirkhan]

Here are some strategies that frequently prevent the random letterboxing/overlay glitch:

1. The playback device should be reset.
Navigate to Preferences > Playback, turn off your external monitor, click OK, and then turn it back on. This effectively "rebinds" the monitor and frequently resolves these sporadic overlay problems.

2. Disable "High Quality Playback."
Try turning it off if it's enabled. When scrubbing or adjusting clips while pushing full-resol output to an external display, some systems choke a little.

3. Try briefly turning off "Mercury Transmit."
Turn Mercury Transmit off, see if the glitch disappears, and then turn it back on using the same menu under Playback. For many users, this resolves strange scaling/overlay issues.

4. Update or reinstall the firmware and display drivers on your dock.
Particularly during live timeline updates, some docks pass the signal in ways that Premiere doesn't always enjoy. For some editors, this exact problem has been resolved by a dock firmware update.

5. Consider temporarily moving the playback monitor to your other external display.
It can help determine whether the dock > display chain is the source of the problem if it doesn't occur on the other screen.

6. Reset the settings for Premiere
To reset preferences, hold Option while starting Premiere. It's annoying, but it frequently fixes strange display bugs.

That sounds more like a redraw issue than a corrupt sequence because it can be fixed by jumping to a different timeline and back.

If none of that fixes it, it may be a newly introduced bug in 25.5.0; in that case, updating after the next patch is released or rolling back one version usually fixes it.

[Paul_WTVT]

Thank you though I have already done 1, 2 didn't apply as it wasn't enabled, I will try 3 and report back. I haven't done 4 and will probably have to ask our IT dept to do that since it's probablty locked behind admin login settings. 5 I've also done and 6 I'd prefer to avoid if I lose settings (but maybe there's a workaround to avoid that?)

I don't think this is unique to the current version either, it's happened intermittently over such a long time I'm either just getting bored of it lately or it's increasing in frequency.