Seems like there's multiple causes then, because the only way I got my launcher to successfully load presets and mods was by doing a factory reset and selecting the keep my files option. It worked, and I haven't had the issue since. My issue likely wasn't that the HTMLs were formatted wrong since everyone I knew could load the same HTMLs perfectly fine.

This worked for me : Goto your arma directory, right click on arma3_x64 for 64 bit or arma3, and click properties. Goto compatibility, and click the "run compatibility troubleshooter" and just reset your settings, test the program, and fixed! At least for me.