Timeline window disappears when exporting

I understand the frustration ... there's several frustrating things in the way Premiere does ... or doesn't ... work with monitors as we users would choose.

My puzzlement with your situation is simple. After more than a decade of heavy use with always at least three monitors, I don't have any clue why you would use the Program monitor by itself rather than Transmit out. 

So I'd love to hear how you prefer that setup ... not to criticize, but to learn. We're all different.

Yes - but I'm having the exact same issue, using three monitors, Left: Timeline, Right Effects, color, and center top: Program Monitor; and I am not using a mercury transit. I'm just using the third monitor as the display for the "Program Monitor" - It still shuts down the timeline during every export. The sequence is this
- If exported and immediately cancelled and reverted back to "edit" panel - evrything reset to their respective locations. 
- If exported and continue toward completing the export/render - then even choosing the "edit" panel does not work and the time line is lost. 

What I do is as a work around I gave a key board shortcut to my workspace - and eveytime the timeline dissapears, I Just Alt+Shift+(1, 2 or 3 whatever its saved as) and it goes back to my prefered layout, with the right windows on the right monitors

This is definitely a bug - because it used to be perfectly fine upuntil the early 2023 updates, and can't seem to remember which one later on caused this.

I'm not quite sure which monitor has which ... so I'll give some observations, having used three or four monitors for several years. And yes, I keep asking the devs to update Premiere's use of monitors, but we ain't seen anything yet. 

Premiere simply gets cranky if the 'main' UI window ... with the Menu bar et al ... is not on the monitor your OS is set to for main UI monitor. Which is a bit of a pain for some users.

Second, it doesn't work "spread" across monitors well, so you have to make Panel Groups for each monitor. And ... you must make sure not one line of pixels gets on a different monitor or there'll be madness. So it's best to leave a tiny, but visible, part of the edge of each monitor visible.

The above means that Transmit Out can never be set (reliably) to your main OS UI monitor.

But if you follow the above practical practices, it normally works fine.