Okay, one more thing before I go:
I’m picking up on what you said about spring tension.
The spring only goes into the back of the face of the vise one way. The spring only connects to the castellated nut one way.
When fitting mine have the vise upside down on the bench. I fit the castellated nut to the spring, that assembly into the face of the vise, then slot the QR Lever in so it is one turn away from being in the right position. I then fit the QR bar into the castellated nut and twist it, so tightening up the QR spring. When the lever is in the right position I slip the end of the bar into the loose QR dog, and then tighten the dog cover down. Then I put the screw in the QR lever to secure the bar.
I’m wondering if you have too much tension? Maybe let it off one turn and see what happens? I’m wondering if the spring is deforming somehow on short openings and affecting the dog? When the vise is more open the play in the bar would be mitigating any deformity?