Hi Jyothi,
It looks like you are facing [PXB-2702] Backup fails when undo truncation log is present - Percona JIRA
MySQL server is supposed to remove the undo*_trunc.log after resuming from crash. For some reason, it leaves this file (orphan). This confuses backup.
We will be fixing in the upcoming release of PXB 8.0.30
As a workaround, you can try to rename them the undo_trunc.log files in server data directory to undo_trunc.log.backup(or any other extension except .log)