Hello @giannaabs!

My first thought is to check dough temperature, and yes, processing time.  This can also often be an oxidation issue caused by too high a level of ascorbic acid.

On rare occasion I have seen the level of calcium propionate in connection with SSL (sodium steroyl lactilate), produce browning blisters on the crust.

if you can provide a picture and a little more detail, hopefully we can help you get to the bottom of this.