Hello @Adarsh.op
Thanks for raising this question with us and choosing Commvault!
When a T-log job runs in CV we will take note of the last Log Sequence number ( LSN ). When the next job runs we check the first LSN to validate we are still backing up t-logs in sequence. If we detect that this chain is broken then we convert the backup to a full as a broken chain results in useless data.
There are a number of reasons the chain can break but the most common is that the DBA team is performing some kind of interactive backups outside of CV resulting in t-logs being cleaned up and breaking the LSN.
If you are still having issues i would recommend a ticket and we can review from a support side with more context.
Kind regards
Albert Williams