I did sizing as well and made sure to degrease the back too. I did hear about others degreasing sinew before applying but have aloso met plenty who don't so I think it depends on what sinew you are using or what bow style you want to do.
But as I mentioned before, these bubbles only appear in the crowning strip of the second layer, not the first layer where it was being applied directly to wood that had been degreased and sized. Not sure if that has to do with the fact I didn't size enough in between layers or if I added too much glue when doing this crowning layer. Or maybe Knox gelatin glue just has a tendency to do this.