Yesterday I sent a transaction with a very low fee (1 satoshi per byte). It stayed for a few minutes in the memory pool and was showing as zero confirmations on both sending and receiving wallets. Then after an hour or so it had disappeared from both, as if it hadn't occurred. I assumed it had dropped from the memory pool as it was very low fee. Today I thought of entering it again but when I turned my computer on I saw (on the watch only version of the wallet) that the transaction had gone through (>100 confirmations).
Yet at some point last night I could have sent it again from the sending wallet.
What could have happened? Could it be that the transaction was still in the memory pool but one node decided to drop it and the wallet (Electrum 2.9.3) reported it as dropped, but then a miner included it in a block and so it was followed by others? And if so, if I had sent it again, presumably the second transaction would have been eventually rejected?