Currently in our environement, the issue persists.
We had an event in January where the Media Agent hung for several hours. It got to the point that our only recourse was to hard-reset the Media Agent. This resulted in a DDB reconstruction, which took over a day in the middle of a weekend when we do most of our Full backups.
More recently, this issue occured again about a month ago, and then again a week later. We had already opened a case by this point.
Per the case notes from the agent:
"If the issue that is occurring is related to dirty pages within Windows, then one of the recommendations is to enable the garbage collection on the DDBs on the media agent. The first recommendation is to configure the key and install the hotfix. You already have both completed."
For that support case, the agent verified that we have Hotfix 1825 for SP16 installed. Additionally, he verified that we had already applied a key (DDBThrottleKBPS) on the Media Agent in a previous attempt to fix this.
The next recommendation from support was to make a change to our DDBs to enable garbage collection. Before enabling, it was necessary to perform compaction on the DDBs - which took them offline for about an hour each.
It has been nearly a month since we've enabled garbage collection, and so far the issue has not returned. I take this with a grain of salt, as we had almost 2 months betweein incidents at the end of 2019 (Nov to Jan).
In short - issue is still outstanding and resolution is pending.
I'm not sure if I noted it in previous posts, but like others - when the MA stops processing requests for CommVault, logging into the server is not possible either. We get stuck at the login screen "Applying Settings." Once the Mutex messages go away, I'm immediately logged into the server.