What could be wrong if you cannot decode an RTTY or other FSK signal even though it is apparently tuned in properly?
Why FSK decoding requires the receiver and software to agree on three things: which tone is mark and which is space, the signaling rate (45.45 baud for standard amateur RTTY, but other rates exist), and the sideband in use. Getting the mark/space assignment backwards inverts every bit, so the decoder prints garbage; amateur RTTY is normally sent LSB, and choosing USB by mistake reverses the tone sense the same way. A baud rate mismatch means the software samples the bit stream at the wrong intervals, so nothing lines up. Because all three faults produce a signal that looks tuned in but decodes as nonsense, all the listed causes apply.
Watch out Each individual choice is a real failure mode, so picking just one, such as reversed mark and space, misses the fact that the sideband and baud rate errors cause exactly the same symptom.
Tuned in but gibberish? Check the three S's: sideband, speed (baud), and shift sense (mark/space).