Errors received attempting to use recorder with Mariadb

Previously had a working up-to date Hassio system which was based on a SD Card & a RPI3b.

Took a full snapshot, and restored this onto the same RPI3b but with a USB SSD drive.

Have already dropped and recreated the Mariadb add-on multiple times to not effect.

When have the following in my config (with specifics removed):

recorder:
db_url: mysql+pymysql://username:password!@ipaddress:port/databasename?charset=utf8

No matter what I do (removing the +pymysql, adding/removing the port, replace the ipaddress etc) - I receive the following error message - pymysql gets replaced with mysql if i change the config:

ERROR (Recorder) [homeassistant.components.recorder] Error during connection setup: No module named pymysql (retrying in 3 seconds)

Mariadb is on the same host - wondering if the snapshot restore is incomplete and missing drivers?

Has anyone seen this before? Any clues on fixing this?

Thanks for the help!
James.