there are a lot of mod types around with different Identification keys. Mostly are M.K. , but there are also M!K!, OCTA, xCHN, xxCH and many more. 15 channels mods have no id key at all!
Maybe fmod doesn’t detect the identification keys above and tells you they are unsupported.
S3M has a really bad format specification IMHO (one thing for all: 24-bit pointers, and I told everything about them!), and maybe some trackers wrote wrong values in wrong positions.
You may try to open them with Modplug player (or even better Modplug Tracker), then resave them in the same format or maybe in a better format (MOD->XM and S3M->IT) and look if they work.
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