lean a/f is a mechanical issue. I guarentee your tune is very rich and conservative. Check for vac leaks/intake/inlet/fmic leaks. Is your fuel pump a hacked fit version? Mine failed some of these symptoms you are describing are similar. Is it still hovering around 14.7 during closed loop operations, if it randomly is spiking under closed loop situations its a fueling issue im betting or a leak. Something mechanical has changed.
Id start with cleaning your maf and pressurizing the system to check for any leaks first. Go from there.
06 TB EVO IX SE stock turbo monster subaru hater