Poop question

Ta

My 11 week old has been on formula only for about 2 weeks (was previously doing only breast milk from weeks 0-8 then formula and breast milk from weeks 8-9). His poop changed from the yellow seedy to green mushy rancid smelling. Now I am noticing the yellow seedy-ness coming back with the green mushy rancid poop. Is that normal? Anyone else experience this?