This could have been caused by a bad batch of Varethane, the finish wasn't fully mixed before application or a reaction with one of the other products used. Also if applied too thick or a second coat was applied before the first wasn't fully dry this can cause a soft finish. Usually the finish will harden with time.
If it is still soft and gummy you will have to strip it and start over with a different finish. Careful stripping could leave the stain intact.