There are several things that can cause a slippery floor after burnishing. First, I would make sure the floor has been dust mopped to remove any fine powdered finish generated by the process.
Next, check to make sure that dust mop treatment is not being applied over the floor, or that the dust mop itself is not heavily contaminated with buildup, including dust mop treatment residue that can be left on the floor. Also, check to see if dust wands are being sprayed with furniture polish causing overspray to drift onto the VCT.
Check for any type of silicone or solvent drifting onto floor, such as WD-40 sprayed on chair wheel bearings, etc. Finally, if the finish has worn off, you may still be able to burnish a shine, but not a gloss. Once the finish is worn, the floors will lose the traction supplied by the floor finish. Only a scrub and recoat can... — Gary Clipperton, National Pro Clean Corporation