Some steep climbs are not detected by ClimbPro just because they are shorter than 500m, even though the slope exceeds 10%.
Most users will agree that going through 400m uphill with 10% slope, which does not meet criteria for climb detection, is more considered as a 'climb' than going through 600m uphill with 3% slope, which meets the criteria.
Maybe the 'minimun length of 500m' criteria is set to reduce load of calculation for detecting climb. This criteria is pretty old since the processor of newer devices like Edge x40 can handle calculations faster than before.
Recently Wahoo just introduced Summit Freeride feature, which is similar to Free-ride ClimbPro, and they considered about these shorter, steeper uphill by setting criteria like this:
I hope Garmin also incorporate shorter, steeper uphills to be detected by ClimbPro.