Question: What happens when a transaction is included in more than one block?
Don't break the forum rules,and no PLAGIARIZING!
Assuming that the block would be valid then it couldn't happen. Transaction can be included in the block only once since it's not possible to spend your bitcoins again.
It's all economics based, where miners only confirm transactions with the highest fees, especially in times where unconfirmed transactions are piled up and impossible to confirm by the next block.
There is no such issue in the Lightning Network since all transactions are settled immediately between two parties as a sort of agreement.