I have some data corruption and was not able to restore the data via backups. It was affecting mainly non-clustered indexes, so after drop-create of the indexes the issues were resolved.
Finally, I have:
Msg 8905, Level 16, State 1, Line 3 Extent (1:896320) in database ID 15 is marked allocated in the GAM, but no SGAM or IAM has allocated it. CHECKDB found 1 allocation errors and 0 consistency errors not associated with any single object. CHECKDB found 1 allocation errors and 0 consistency errors in database 'db_name'. repair_allow_data_loss is the minimum repair level for the errors found by DBCC CHECKDB (db_name).
I want to find which are the extent pages and then to see what's the data in these pages. Then, to decide to run the CHECHDB command with repair_allow_data_loss or save some data if possible.