I imagine that's just because of potential flow restriction, I can't
see it affecting the connector "grip".

To the OP, I'd just try a different hosepipe fitting, preferably
without the waterstop feature.

The problem with the waterstop is a spring loaded N/R valve. Since
the pump sucks it forces the valve shut & stops the flow.




I don't think so Dave, The Water Stop is held open by the male part pushing
it off the seal face.

The OP probably just has a worn out or imitation Hoselock fitting. I had
some Aldo ones once that were not very good when used with a proper
hoselock although okay with each other.