Ok, so I did some more investigating and the problem appears to be either Reshmaan itself or this specific mission- HWS saves just fine with vanilla factions on Altis, and your Chernarus missions save even when I use the same factions and settings as I did here. I was using CFP factions (which use just CUP assets)

First of all, just want to say that I love all your HWS ports- it's nice to be able to play it on so many maps without having to worry if I set it up correctly!

However, saving appears to be broken in this mission. If I save and then try to reload the save, it says that I'm missing what appears to be a list of CUP Maps files- even though it was running the mission just fine beforehand and I have all of the CUP mods enabled and properly updated.