SQLserver writer is not listed in vssadmin list writers

My name is Toni, i am a system admin and not a dbadmin, i am playing this role for now because our dbadmin left.
I have an sqlserver 2016 having 5 instances, and the databases are backed up on daily basis via commvault backup software.

2months ago the dev team asked me to add a new instance to the server, so with the help of google i created the instance, but from this time the backup start failing (unable to create shadow copy during backup). I start doing my research and the majority says that there is a problem with the sqlserver writer.
I opened cmd on the server and type this command: vssadmin list writers and found that the Sqlserver writer is missing.

Also i have an issue but i think it has no impact on what's happen, and the issue is that i am not able to access one of the instances installed before by the ex dbadmin .all the others instances including the one added by myself can access them with no issue.

NB : our ex dbadmin has created also a double backup using maintenance plan to make a local backup for safety, and since i installed the new instance all the maintenance plan keep working fine except the instance that i can't log in to, the maintence plan keep failing from this date.

Can someone please help me to solve this issue, as it is been a while that this issue exist.

Thanks a lot

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