Using Smart Control, one need to do both assignment: the controller and the parameter.
1-Assign/learn the fader/knob from the controller, which gets detected by Logic that you can see
2-Assign the target plugin parameter(s) you wish to actuate with that fader/knob you assigned in step 1
If that doesn't work, perhaps you could pay a visit in the Controller Setup window to ensure that no unwanted controller had been unduely installed. That happen sometimes, as Logic usually detect and automatically a controller in there, which may cause issues with other intended installation(s).
Also worth checking if your controller is(n't) enabled in the Control Surface / MIDI Controllers prefs
LogicX 10.5.1 ( & 9.1.8),MainStage3.4.4
MBPro 17", Core2Duo, 8G, OSX 10.12.6
MacPro, Xeon 6Cores, 64GB, OSX 10.15.5
ULN8, MOTU MIDI TP-AV, C4, MCU Pro, KorgNano, Novation SLMkII
AAS, NI, Celemony, Spectrasonics, Korg, etc...
PC, iPad3(V-Control & LogicRemote), AtariST(Notator SL), Several vintage gear