Getting brownouts when using MCU controlled P-FET to switch power to another board
I tried adding a 1K resistor to the gate and adding 2.2uF (all I had on hand) capacitor near the transistor but the issue persisted. However when I removed the 10uF cap on the second board everything started working. 

The large value was a holdover from a previous version of the design where the second board had a lot more components on it. I'll either downsize it or remove it completely going forward.