I think I see this too. Every other startup already has problems even launching in the first place (some other issues mention this). But when steam does start, it appears to alternate between last position, and center of screen/monitor.
edit:
related? https://github.com/ValveSoftware/steam-for-linux/issues/9742 > https://github.com/ValveSoftware/steam-for-linux/issues/9660
Your system information
Please describe your issue in as much detail as possible:
Steam windows seem to lose much of their X properties for a brief moment before closing. While not too troubling on normal desktop environments, this causes some rather annoying issues on tiling window managers. Any time a notification from steam or context menu in the friends list closes, it briefly loses its floating status, causing some jarring movement on all windows on that workspace.
Alongside this, it seems those windows will sometimes steal focus for the brief moment they lose their class. Sadly, I haven't been able to get a capture of what information those windows provide, though through trial and error, I know at the very least they lose their class and title.
I've been able to mitigate this somewhat in i3wm with the following rules, though I still have blank black boxes pop up in the center of my screen:
Thank you, and I hope this helps!
https://github.com/ValveSoftware/steam-for-linux/assets/3003520/0cac74d3-3e3a-43bc-ab3c-a80a3fea66ae