What material are they made with? If they’re Reaper Bones figures, the problem may be the material rather than the varnish (that semi-soft plastic doesn’t play well with some spray paint/varnish - maybe due to sprays often being enamel-based?).
I haven’t come across a super effective cure for ongoing tackiness. I probably would try a brush-on acrylic varnish to see if that ‘seals’ it. It might not work if the problem is enamel in the spray varnish reacting to the figure.
If the figure is some other material, the problem is probably that your varnish is curing very slowly- no idea what to do about that, other than keep waiting.
I hope someone posting here can provide better advice and you can resolve the problem, it’s a huge drag when something goes wrong with painted figures!