Okay, let's start: Turn your Kemper on first... (sorry, couldn't resist afer your last remark... and humour always helps in such situations....)
Now seriously: Welcome to the forum and have fun with your Kemper. Recording and re-amping via SPDIF works like a charm for me. So let me try to help by just firing out some thoughts or questions which may help:
- Which Kemper? Toaster or Rack? Then the Kemper needs to be Master in the SPDIF clock configuration! Stage? Then it shouldn't matter but one of the units needs to be Master, the other can't be Master then.
- Wired the SPDIF correctly? Kemper out to Clarett in? Kemper in to Clarett out in case you need clock signal from the Clarett?
- SPDIF output volume should be at 0.0 per default.
- Tried different profile(s)?
- Have you tried to set the SPDIF out to Git / Stack for instance to see if signal comes then? Advantage that the pure Git signal would come then as well and then the profile would not play a role in the game.
Hard to find more for me as it is pretty straight forward - at least in the Kemper itself. As I don't have the Clarett and Logic I can not speak for that. Have you made sure that the routing in the Clarett is appropriate? And that Logic is grabbing the right input channel, i.e. the one coming from SPDIF in the interface? Routing can be complicated.
Fingers crossed that you'll figure it out quickly....