There are fuses (some user changeable) on the YSF22 and rotary switches. Check the black cables (should be 2, since you have FSU) that go from the YSF22 to the YSF21 (CN201-CN211, CN202-CN212). Make sure that you have the terminating resistors installed if this is on R1.
Another idea is since you have FSU, look in the Machine Safety Logic Circuits. There may be a rung where something is preventing a mode change.
YSF22 fuses are good(Changed board just to be sure). YSF22 to YSF21 cables are checked and terminators are connected.
What could be related with Machine Safety Logic Circuit? Can you explain more about it please.