This confuses me, because I thought I was setting the lock time to a block height of 1, which should have already passed.
You talk about the last field in a tx (nLockTime), or the stack item before the CSV command?
I think that nLockTime must not be set to the „relative“ block height of one... could you show the raw tax, so far as you got? The wiki explains to set nLockTime field to a higher value than the stack element for CSV, see here:
https://en.bitcoin.it/wiki/Script
I meant I read somewhere (just can‘t find the link), that LockTime cannot be the default „ffffffff“, it must be s.th. else.