Migration manager fails 7.5 -> 8.1

[bmeshier]

It only happens on this specific server, no problem elsewhere:

Error during dump file retrieving.
Remote agent failed with the following stderr messages: 16:41:40 INFO FileFinder: pwd resolved to /bin/pwd
16:41:40 INFO ------------------------------------------------------------
16:41:40 INFO FILE storage initialized.
16:41:40 INFO Base directory: /var/qmail/migration/supervisor.6351
16:41:40 INFO Gzip bundles: yes
16:41:40 INFO Bundle split size: do not split
16:41:40 INFO ------------------------------------------------------------
16:41:40 INFO ------------------------------------------------------------
16:41:40 INFO Migration status reporting initialized.
16:41:40 INFO Status file: /var/qmail/migration/supervisor.6351/dumping-status.xml
16:41:40 INFO ------------------------------------------------------------
16:41:40 INFO FileFinder: tar resolved to /bin/tar
16:41:40 INFO New connection: mysql DBI connection. db psa, user admin, host localhost

...
...

16:42:54 INFO Client 'lnbih2c' is started
16:42:54 TRACE SQL: SELECT * FROM clients WHERE login = 'lnbih2c'
Undefined subroutine &Logging::warn called at Encoding.pm line 24.