Can confirm in 2.3.580 (New Windows App). Repro steps also work for MCL-22745, so the underlying issue seems to be the same.

Going to add that, rarely, the location and size fully resets and it opens in the top-left corner of the left most monitor to the default size

This occurs with both currently updated versions of the launcher (from the website and from the MS store).
Everything is up-to-date.

PS: I've updated the description to be more accurate to the current bug.
PPS: I'm not considering it a bug that when you snap the window to the left edge of the left monitor that when you relaunch, it's not snapped to the left edge; it's on the left side where you would expect it, but only with the left monitor.
PPPS: I've tested with other programs and they open as expected: in the same spot you closed them, even if straddling across two monitors.

Hi there! 
Could you answer few questions regarding this issue, it will help with the investigation: 

• Does this issue still occur on newest version of Launcher?
• Have you tried to install Launcher from the minecraft.net website/MS store?
• Is your Windows and associated apps (Xbox app, MS store) up-to-date? 
• Are your graphic card drivers up-to-date?

This ticket will automatically reopen when you reply.

Bug is 95% fixed. Game Output Log closed on monitor 3, appears on primary monitor next launch, if too close (within apx 10 pixels of) to edge of monitor (including snapped to side). DOES keep custom size now.

My setup: monitor 1 on left, launcher loads here; monitor 2 in middle, set as primary, game launches here; monitor 3 on right, game output meant to load here.

I realize this is likely a very niche case, but it is technically still a bug. Will edit bug for clarity and include screenshot of my setup and the result from game launch as well

I would, please, for being the reporter.

I would probably say "Game Output Log window" in the bug section to avoid confusion with the game window itself?*

By previous versions, I mean previous launcher versions with both the old and new launcher. I think the previous version of 2.1.932x it worked (I got the version history off the wikipedia). It definitely did work within the last month.

*edit - I realized I can edit this one, so I made the change

I have moved the part about the launcher window not remembering the position to a separate report (MCL-12596). Please let me know if you want to become the reporter and keep the report up to date.

I have also rewritten the report, I hope it still includes all relevant information.

You wrote that it worked correctly in "previous versions". Do you mean the old Java launcher, the other newer launcher or previous versions of this one? If so do you know the exact version?