Try to re-render them on a gm_construct map (right click on a broken icon, select Re-Render, select All icons)

Also, what GPU do you have? Are you using the latest video drivers? this could be a sign that the gpu is dying, or when the game crashes during the icon rendering process - the result can be the same.

And also avoid Alt-Tab from the game, it often breaks random things if the game is running in full screen mode

Re-rendering fixed it.
Intel(R) UHD Graphics 630 is the GPU.

The only addon folder with this was the Starship Troopers one. Everything else works fine and I've had no problems since. Must have been a fumble during the installation process I guess.

I don't recall Alt-Tabing from the game, though I do run in full screen mode. I do use shift+tab to bring up some player info as in screenshots as I usually want to check if I got the screenshot right. But I don't think I used Alt-Tab before.