Hello! So we recently replaced our blown engine. Bought an engine from Switzerland(the car we bought engine from is a stage2 + downpipes). After the replacement, I went to our local tuner to flash the new engine ecus to ours. He said the tuning is very promising. Our car is m5 f10 - 2012, the engine we put in is from car 2016. Everything is perfect, the car is running so smooth, but these dtcs are disturbing also the check light is on.

118010 Mixture Control 1 and 2, Cross-Bank: Fuel-Air Mixture too Lean
118501 Mixture Control 1 and 2, Mixture Too Lean, Large Deviation

Anyone know what can cause this, also I didn't have the files of the car but can contact the local tuner to send them to me, If needed to be shared.
Could it be 02 sensors? The car is running catless downpipes.
Thanks in advance!