I have a transaction with nonce #30, because of low gas price this tx is dropped while I checked on Etherscan (case #1 dropped transaction not dropped and replaced #2 ref). Before this transaction is dropped, I have also checked my 2 physical node geth, both of them response full detail of it by using eth_getTransactionByHash. But after dropped status for a period time I recheck again, eth_getTransactionByHash returned not found this transaction and also null receipt returned by eth_getTransactionReceipt.
Next 3 days, my friend does not notice this case and create new transaction with nonce #31, cause I have never met this stituation before, currently my program will increase each nonce after a transaction broadcasted on network. Normally, I should create a new transaction with nonce #30 cause previous tx #30 is dropped and this nonce is not filled. But when I create transaction with nonce #31, previous dropped #30 transaction is automatically rebroadcasted (not by anyone in my team) and status changed from dropped to pending then became success for a short time because of network fee reducetion.
I have tried to read ref carefully but not found dropped transaction can be automatically rebroadcasted, I have also searched but not found any related information conflict to this case. I hope someone who have faced this case can explain and confirm it, thanks so much.
Previous dropped transaction nonce #30:
Now it becomes success transaction none #30 same hash:
Transaction nonce #31: