Mute switch not working after housing replacement

Hi all,

I have recently completed a housing replacement on a 5c and all functioning well with the exception of the mute switch.

I am not sure what is going wrong. The mechanical switch on the flex cable functions fine put the plastic silent button doesn't seem to be latching on to the mechanical part.

The plastic part isn't defective or misshaped because I have tried with known working parts and the issue is the same.

Should the plastic part click into place or just rest on the mechanical switch?