I was trying to compile the different weights of my typeface and I ran into a strange error. The Regular weight compiled without issue (as did the Regular Italic). However, the Semibold and the Bold ran into "[FATAL] Stack underflow".

What is strange is that all of the class information and Opentype feature information is exactly the same across all of the weights.

Why would it compile fine in the regular weight but not in the Bold or Semibold?

Thank you very much for your help!