LEARN will only work for controllers we do not already have a MAP for. Since we natively support the Beatmix 2, the map is the map. Furthermore, the only way (on any controller currently) to delete cue points is to press and hold the CUE button you wish to clear. That will not always be the case, but it’s how the function works in DEX 3 by default right now.
I’m not sure what you’re asking about cues/loops, but they are not tied together. Loops are automatically quantized, so they snap to the nearest beat automatically.
SYNC will work, but is crossfader dependent. Meaning, you want to press sync on the opposite deck to where the crossfader position is. If it’s past the 50% (neutral) position, say on the deck A side, you would press SYNC on the deck B side to sync. It will not sync if the crossfader is on the side that you’re pressing sync on. Someone difficult to explain, let me know if this makes sense!