bubbles are cause by;1. not enough adhesive 2.too much adhesive 3. seam from the plywood flooring expanding and contracting. and various other things. What I've dont in the past is use a flooring sirenge, found at any flooring specialist outlets, get the proper adhesive, fill up the needle and poke through (in an inconspicuous area e.g. pattern lines, if possible) and apply the adhesive. You may have to do this in three or four areas along the bubble, then use a hand roller to distribute the adhesive injected in the bubble, clean any access glue using proper cleaner, then use a seam sealer kit and cover the entry points you made with the needle. The roller can be rented at a tools rental shop..