Sometimes the water used is so hard tapping, or any other form of agitation, is not enough to get rid of air bubble. A very small amount of wetting agent cures it effectively. I use a couple of drops, too much takes it the other way and you get foaming.
In a couple of previous posts on this subject I added some photos, I tested various methods of trying to eliminate air bublles a few years ago in Turkey where my local water has a high salt content. I did visual inspections of the film in the tank and the air bubbles were stubborn many remaining after vigorous tapping, inversion etc, The only agitation that worked reasonably well was the stick thing Paterson tanks use for rotating the spiral in the tank that removed the most air bubbles. The drops of wetting agent meant they went immediately.
It's worth noting film emulsions often contain surfactants (Wetting agents) as an adjunct to help in the coating process, some have a bit more than others while we are only talking very small quantities it does make some films slightly less prone to air bells than others.
Ian