I purchased that vise last year, the jaws were atrociously misaligned. I went back to the store and opened the other three that were on the shelf, all were terrible. I returned mine and eventually got an Amazon gold box deal on a Yost 4”.
I had a shity old Harbor Freight Vise that the base wouldn't tighten up. I ended up removing the two side handles that you used to tighten by hand, and replaced them with half inch bolts. Now I tighten my base with a 3/4 inch wrench instead of my hand and it gets nice and tight. Simple modification made all the difference.
I've got an old Columbian vise that is giving me the same troubles. I've been thinking about how I can correct it and I'm going to try putting a piece of relatively rigid rubber, cut to size, between the vise and the base. That way it has something to bite into when tightened down. I haven't tried it yet, but I relatively sure that it will fix the issue.