UNABLE_TO_LOCK_ROW:unable to obtain exclusive access to this record or 1 records

Please attempt again to solve the issue .

Basically,  when a record is being created or updated, it is locked so that other users cannot update the record so we get this error

Also refer-

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/langCon_apex_locking_statements.htm