Small Air Bubbles In Oil

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After I did an engine swap, I fought out that there are small air bubbles in on the dip stick after a moment of running. They are not too tiny, visible.

I thought bubbles are building up if the oil level is too high, but mine is right below full. and I used 10-40. and it's a 5AF J spect corolla engine. I don't get it.. cheap oil filter? it is cheap, but could that be why?

or it's just too much dirt inside and it takes time to rinse them out?