did you restore database on some other server.. ?

I have created a job with the following code to track whats going (run every minute). above options are good however you have to check em daily/hourly/ whenever,  I found...

there is much more to learn 
sqlcmd.exe and/or SQLCMD mode

https://docs.microsoft.com/en-us/sql/ssms/scripting/sqlcmd-use-with-scripting-variables?view=sql-server-2017

is email setup correctly.. 

use msdb
go
SELECT items.subject,
  items.last_mod_date
  ,l.description FROM dbo.sysmail_faileditems as items
INNER JOIN dbo.sysmail_event_log AS l
  ON items.mailitem_id = l.mailitem_id

open case with vendor

another one.

DECLARE @path VARCHAR(8000)
declare @trcfile table (path varchar(8000))
declare @loc varchar(8000)

SELECT @loc= 'dir /B "' + replace(cast(SERVERPROPERTY('ErrorLogFileName') as varchar(255)),'ERRORLOG','') + '*.trc"'
insert into @trcfile
exec...

deleted

not really, the best you can get is what is in the default trace using query below or from  disk usage report 

SELECT TE.name AS [EventName] ,
   v.subclass_name ,
  ...

one port per instance... per box. , you can not have the same port number if it is being using by something else (including mirroring), and since instance are located...

can you try connecting using listener IP instead of listener name, after fail-over to see if works..

I would say try on your test environment and let us know the results, I too want to know if it works, if it does not then you might need 

I suspect after the fail-over if DNS does not get updated you wont be able to connect because the listener will be pointing to old IP, I have seen this...

when you assign IP address it is going to be there, heart beat or public network doesn't matter, use host file on your backup server and see if it helps.

spend some time and you will find out, I use separate drives  regardless of SSD or spin drive just to maintain standard in environment. it does make things easier, I...

query master.dbo.database_mirroring table to find out, or may be create a snapshot on sec mirror and compare ..