Microsoft didn't find anything?

Hi Hawg

There is a PASS video about TLS 1.2 made by a microsoft sql tiger team.

https://youtu.be/KrPp-G_1aAk

You can start here

https://www.sqlservercentral.com/blogs/t-sql-tuesday-050-%E2%80%93-automation

https://www.sqlservercentral.com/articles/sql-2008-spcu-patching-through-windows-scheduled-tasks

1.Windows Cluster 2

What kind of cluster?

2.Availability Group with four databases (2 syncronous and 2 asyncronous)

Where are the availability groups failing over to?

Do you have CDC enabled on a database which is replicating to Oracle?

try using FQDN.

If you lose a VM and you have AG configured in automatic fail over your secondary will be a primary.
if you cannot bring up the VM then you...

try this:
DECLARE @command varchar(1000)
SELECT @command = 'USE ?
DECLARE @mult float = 8192. / 1024 / 1024 / 1024;
SELECT df.physical_name AS FileName, df.name,
MAX(CAST(df.size AS...

You might be having this issue FIX: TDE-enabled database backup with compression causes database corruption in SQL Server

What's the number of databases and their size?

When you get "Unable to access database 'XXX' because it lacks a quorum of nodes for high availability. Try the operation again later." it means your servers are not communicating...

check database mail log and see if emails are being sent.
sometimes the profile security is not setup properly.

Check if those 4 listeners were added in AD as computer objects.