Aren't you using amcrypt?
The warnings around the deprecated key derivation are around for a long time now: https://github.com/zmanda/amanda/issues/112 At a restore test I noticed that adding that one option `-pbkdf2` breaks restoring older archives encrypted without the option: https://github.com/zmanda/amanda/pull/149 So either have "STRANGE" amdump reports all the time or break restore ... - Maybe someone is motivated to come up with some clever if-clause for the restore part. upstream development seems non-existant to me, latest commit at github is from 28 Nov 2019.
