As it stands you got two seemingly contradicting answers to your question. They are actually both sort of correct. You can indeed try to replay a transaction f

As it stands you got two seemingly contradicting answers to your question. They are actually both sort of correct. You can indeed try to replay a transaction from one chain to the other. Everything in the transaction is still valid. It will be propagated by the p2p nodes as they just perform crypto sanity check. It doesn't mean it will be included in a block though. For the replay to goes through and be included in the blockchain, there needs to be at least as many coins held by the address in the other chain. This is usually not the case for addresses created post-fork. However, all addresses that had coins before the fork are susceptible to this issue. There are guides to "split" the coins so that you can safely separate them and hold them in brand new addresses that have zero balance on the other chain. It's a painful issue that was raised before the fork but had been downplayed by pro-fork supporters as the old chain was supposed to die quickly.