Yes, chickens have a perverse penchant for eating Styrofoam, silicone caulk, wall insulation, etc. Usually, as long as the particles are bite size, it passes through the digestive system harmlessly. However, if a great quantity is consumed, it can result in impacted crop. Generally, you can determine the nature of the crop contents by feel.
As for air or gas being a problem, unless its an air sac that is overfull and inflamed, other gas or air should be able to find its way out of a crop from natural movement by the chicken. The crop is not sealed so air should escape on its own.
Have you tried an Epsom salt flush yet? That's what I recommend when a crop issue fails to completely resolve. Chickens tolerate it well. The protocol is one teaspoon of magnesium sulfate dissolved in half a cup of warm water and tubed directly into the crop twice a day for three consecutive days. It flushes out any yeast remnants as well as most leftover impacted material. Then if that fails, crop surgery may then be required. But try probiotics after the final flush. Restoring good microbes in the digestive system may take things to completion.