I'm definitely a few years late to the party, but just ran into this issue in 2022.. It's strange, in cleaning up and removing older versions of acad, I somehow broke my 2022, regardless of my STARTUP variable.
Oddly enough, if I used '2' as my startup value, the ribbon wouldn't load, but the startup would. (The option to toggle the ribbon wasn't present, but that could be a default behavior as the ribbon hasn't a reason to be active yet, anyways).
Also, the UI redraw seemed to chug along using some interesting window 7 "aero" graphics to load up the command line and tabs, not the newer slick gray ones that I've seen 2021+ have (I should note I'm on Windows 10, here).
Additionally, all of my pinned, but collapsible side menus (Layers & Properties on the left, and Xref's on the right) would auto-populate and not collapse until I hovered over them indicating that acad needs a "mouse off" flag to dismiss the menus.
Very interesting indeed, I never had the Design Centre open, either and I checked my default template setting (which were empty), so I'm not entirely sure which template acad wanted to open.
My current fix. Leave 2022, and download 2023. I'm not sure why, but some underlying code seems to have mended itself (or hasn't been broken by me yet :p). Note to self: Leave 2022 until 2024 is ready.
Joking aside, if anyone else has a workaround for future users, or possibly me next year it would be appreciated! (I could clear all my settings with the "great reset", but I'm trying not to do that as reconfiguring everything takes a decent amount of time, but that sounds like a "me" problem!).
