Hi Andy,
Thanks for your reply
It'd help if you posted a datasheet, or some other link about these connectors - so we know what you're actually talking about

I don't have the datasheet for these connectors these connectors are 2.54mm pictch Single In Line [SIL] connectors with 0.65mm2 cross section area of pin and 28AWG wires.

Are you sure that it's the connectors that are at fault?
Could it just be incorrect assembly? eg, wrong sort of wire, wrong tooling, wrong setup of tooling, wrong operation of tooling,...
Yes, This is certainly a connector problem I have tested when carefully/tightly held in some position it works well but when even slightly moved it doesn't. Whats the use of using such connectors that doesn't even tolerate slight movement of wires. I don't have any information about tooling used since I purchased crimped ready made connectors.

Thanks & Regards,
Prahlad Purohit