Confirmed transactions lost in my synchronised node
There could be a few possible reasons for this:


The most likely problem is that you don't have -txindex=1 enabled. By default, the core client doesn't keep track of all full transaction details unless you tell it to with -txindex=1 when starting it. If you want to maintain the full index, shut down and restart with that flag. It will give you a message about needing to reindex everything, that could take a little while.
It may also be possible that one of the daemons was actually in testnet, unintentionally. Make sure they are both on the same network.


The daemon will keep an index of full transaction data for all of your own wallet transactions. That might be why one of your nodes knew about it and the other didn't.