Hi,
from the attached backup log I do not see any error, although I agree that there has not been much backed up. What was the exact backup statement - maybe you have performed just a 'save pages'?
Have you tried to do a recovery test on a different system with that backup?
If you want me to look further, please create a 'diagpack' archive of the MaxDB log files (dbmcli -d <db_name> -u <user,pwd> diag_pack) and upload it via:
https://mdocs.sap.com/mcm/public/v1/open?shr=wEwYg_VA7dJZKVw5BjzSBij_AXYayoChNHmP26TExog
Thorsten