This is best to be handled by the WRC. Please contact support@intersystems.com and provide the full cconsole.log as well as the timing of your attempted startup and details of what you deleted, how, and when.

For what it's worth, my best hypothesis based on the snippets you provided is that you have custom startup code that isn't completing (possibly due to whatever you deleted), which is blocking startup from continuing.

Just noting for anyone who refers to this later that this will also be fixed in IRIS 2019.1.2 in addition to 2020.1.1

Calling into IRIS won't work if the instance is hung, so the only way to detect that is something external to the instance. Take a look at 'iris qlist'. You can get more information from 'iris help qlist', but here are the basics:

Syntax:
        iris qlist
Description:
        Quick list InterSystems IRIS registry information for all instances, in a format suitable for parsing in command scripts.

To add to this, given that you're concerned with security and want to use TLS 1.2, you should strongly consider upgrading, as 2012.1.2 has a number of security issues that have been fixed over the years.

I just want to note that 2015 kits are not available for download anymore, even for supported customers. If anyone has a specific need for a 2015 kit, please contact the WRC.

Are the two mirror members functioning as primary and backup? No members will even attempt to connect to the arbiter until you have a primary and an active backup (because that is the only situation where the arbiter is used). If you do have a primary and active backup, and they aren't connecting to the arbiter, I'd suggest contacting the WRC so that we can take a look at this with you.

Is the database journaled? Remote non-mirrored databases on mirrored ECP database servers can only be mounted read-write on the ECP application server (in this case the reporting async) if the database is NOT journaled on the database server. This is documented here: https://docs.intersystems.com/latest/csp/docbook/Doc.View.cls?KEY=GHA_mi...

"Select the database you want to access over this ECP channel from the list of remote databases. You can select both mirrored databases (databases listed as :mirror:mirror_name:mirror_DB_name) and nonmirrored databases (databases listed as :ds:DB_name); only mirrored databases remain accessible to the application server in the event of mirror failover. When the data server is a failover member, mirrored databases are added as read-write, and nonmirrored databases are added as read-only, if journaled, or read-write, if not journaled; when the data server is a DR async member, all databases are added as read-only."

I don't know the answer to this, but since you haven't gotten any responses here, I'd suggest opening a case with the WRC so someone can investigate it fully. Please include the $zv string from both instances involved, as well as the location of the installation (as I suspect that is relevant to the problem you're seeing).

This isn't enough information to answer definitively, as we don't really know whether there is a limitation on the client side or the server side. You should check IRIS' messages.log file. My best guess is that the errors may be due to running out of licenses. Either way, I think it's worth engaging the WRC on this, as a lot of setup-specific information is going to be required to get to the bottom of it.

That routine ultimately uses the same API under the covers: ##class(SYS.Mirror).BecomePrimary(), which forces down the original primary.