Yeah if you think you may have run over something, especially check the wiring and sensors for the rearmost pair of O2 sensors (behind the cats). They're pretty exposed, I'm not fond of the design there.
As far as the MAFs go, when they're dirty/oiled it can take a while to throw something like P0157. What triggers the code is that it's trying to use the MAF input to verify the response curve of the rear O2 sensor, and after a while of driving it ends up eventually blaming the rear O2 sensor's response curve when the MAF is actually the one at fault more commonly (assuming no damage under there).
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