[Redux]

Looks like CO2 entrapment caused by the HDI catalyst reacting with moisture, possibly from the compressed air source. You might want to pick up a desiccant dryer and see if that helps.
Edit:
Is the product you’re using a single component moisture cure urethane or non-MC 2K urethane?

 

[Redux]

I am using MIL-DTL-64159B Type II 2K Waterborne Polyurethane CARC. Also what would you recommend for a desiccant dryer for a 165 psi 33 gallon compressor

Any decent 3 stage unit should help, however with a 33 gallon tank you also might consider an aftercooler. It’s also important when storing the catalyst to spray argon or nitrogen into the container before resealing which will prevent atmospheric moisture contamination & CO2 gas. Another consideration is to allow the material to rest 10 minutes or longer after catalyzing which will allow the initial blast of CO2 to escape from the mix.