These four missions bring their own custom terrain textures, and the path to those textures had gone out of date, so the game couldn't find them anymore. Instead of showing the intended ground, it had nothing to draw there, so it fell back to the glaring placeholder pattern players have been reporting for a while.

That's now fixed. The deployment chain has been corrected so it always points to the right path for each mission's own textures, and the fix has been checked thoroughly. It was checked against versions the community had already patched manually, and by loading the missions in-game, with several players confirming the terrain renders correctly and nothing else broke in the process.

If these missions put you off before, now's the time to give them another shot. Load one up and see the difference for yourself. Have fun out there!

Thanks to Seraphim-Noob and Brutus5000 for fixing this Bug!

Full technical details are documented in the pull request.