Near as we can tell, there is an airplane (or two or three) that has something "off" in some part of its config. s7rikeback spent several weeks going through them all and straightening out the configs so that all planes are consistently done. If this was the problem, it should "fix" the issue. We have been adding a Save and Load sequence to the testing paradigm, and that is helping us root out other issues also. Nine times out of 10 though, if a Load fails, it will have involved one of the planes in the "scene" of the Save.
All that said, it must be remembered, that when activating FotRSU, you ~must~ clear the Save folder contents, so that there is no corruption from previous versions of the game. Unless you've used MultiSH4, the default path is "C:\Users \UserName \Documents \SH4". Another thing, and I don't know if this is just my computer or not, but on my Windows 10 machine, I have to select all files in the SH4 folder (use the <Ctrl><A> combo), and then right-click and use "Properties", then in the "Read-only" attribute, clear the little tick box and "OK" it, and for all sub-folders and files, then try applying the FotRSU mod. My Windows 10 ignores and runs over all of my user changes on a daily basis, and that is one of the most irritating...
