I guess the catch is not central in the hole when screwed in fully, if it's what I'm thinking of...I had a fiddle with the clips on the cupboards, which open OK, but don't lock. My MH is a swift conversion of a Ducato panel van.
It turns out that if you loosen the screws that hold the clips to the door - just a bit - the things work properly. If the screws are tight, they stick. Absurd, but true.
I thought this might be useful to anyone with the same problem. But then, I'm a newbie, and this solution may be famous.