As I group 1 boarder I was recently forced to gate check my bag as it was ‘too big for this type of a/c’ (A32N). Group 4s and 5s later boarded with bags at least the same size as mine. The bag in question had also been used on both days prior to this incident, and for 2 subsequent flights since with no issues. Seems that there’s no consistency in enforcing the rules.