extract fatal error

i'm trying to make incremental backups with delta sig in a script

first full backup runs fine:

dar --create "../${1}-${dd}-full" --delta sig --compression=gzip:5
--hash=sha512 --slice=2G

then the incremental backup seems to run fine:

dar --create "${1}-${dd}-incr" --ref="${dar_prev_name}" --delta sig
--hash=sha512 --slice=2G --compression=gzip:5 --quiet --fs-root
"./${dd}/"

with no errors reported

however, after testing the extraction of the archive:

dar --extract "${1}-${dd}-incr" --ref="${dar_prev_name}" --fs-root
"${dd}/temp-${1}-${dd}-incr/"

i get:

FATAL error, aborting operation: The archive and the isolated
catalogue do not correspond to the same data, they are thus
incompatible between them

what am i doing wrong?