Comment 84 for bug 1447282

@diwic - I agree, there have been problems in multiple places causing this.

Yesterday I sorted out one of them. If you have swap on a GPT partitioned NVMe or MMC drive, ecryptfs-setup-swap isn't correctly marking the partition as non-auto-mounting, which leads the the user erroneously being prompted to enter a passphrase to unlock the swap partition.

I filed a bug about this and have a merge proposal ready for review:
https://bugs.launchpad.net/ecryptfs/+bug/1597154

This bug has been present in ecryptfs-utils since the original GPT auto mounting issues was fixed, but not that long ago in 16.04 it didn't result in being erroneously being prompted to enter a passphrase to unlock the swap partition. Some some recent-ish behavior change elsewhere has re-exposed this (I'm guessing a change in systemd).