I think it was because my ash catch was not vented well enough so the fire was not breathing. I vented the ash catch better.
You don't need to drill any extra holes. (Sorry cfarmer to disagree) You just need to let the bottom vent breathe properly and not get built up with ash. What exactly are you calling and using for an "ash catcher". Are you familiar with the upside down tuna can method for protecting the bottom vent from plugging? In my opinion the 1 bottom vent of the silver is way easier than having three like the gold.
Something else... What type of charcoal are you using in your mini? noboundaries has a very informative thread on charcoal and the comparison of the volume of ash produced by the main brands. It is quite convincing what you want to use. It made a HUGE difference for me.