Putting the pan on the stove to heat it could cause cleaned
surfaces to become oxidized. Can you suspend it above the
burner to heat it up?


Ecnerwal wrote:

Despite the fact that you are sure that you've cleaned everything
perfectly, evidence (tin flowing over areas of the pan) would suggest
that you have not, or that you have allowed them to become oxidised
again after cleaning. More heat is more often a problem than a solution
in soldering (of which tinning is a specialised branch) - in fact,
overheating areas is one way to make them not take tin.