Added Internal Hard Drive Identified as "Removable" by BitLocker

You can try this link, to see if this solves your problem
https://social.technet.microsoft.com/forums/windows/en-US/ef409ece-50b3-4353-b220-7f3436e7d5d4/internal-hard-drives-being-marked-as-removable-for-bitlocker-to-go

Yes, I had seen that.  However the description:

Install the Intel SATA drivers or add the DWORD TreatAsInternalPort in the registry to each Controller entry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\storahci

Didn't resonate very well with me.  I didn't find anything there that seemed to match with "each Controller entry".  So I was/am stuck.

You can look at HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\storahci\Enum, however, following Natty's link, it also says to install Intel Rapid Storage Technology. I would start with that first.

I guess I only implied that IRST is installed and sees the drives as they actually ARE.  "Port location internal".  So that seems no help.

Looking at HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\storahci\Enum doesn't help me because \Enum doesn't exist.  Only Parameters\Device and Parameters\PnpInterface and StartOverride keys.  If I were to add an Enum key then I wouldn't know what to do with it re: "each Controller entry".

Should I mention that the system is using Secure Boot and also won't boot from CDs, etc. (ROM)?  These controls are separate and interdependent.  I doubt this matters....

I now saw you already had IRST installed, my bad.

The controller is the one that tells Windows if a drive is fixed or removable. It's strange that you don't see anything under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\controllerdriver w.r.t. each controller entry. An example of one of those is like this:

HKLM\SYSTEM\CurrentControlSet\Services\msahci\Controller0\Channel0
HKLM\SYSTEM\CurrentControlSet\Services\msahci\Controller0\Channel1

In the Channelx keys is where you add that REG_DWORD key. Do you see anything like that?

There is no msahci key

If you change the msahci key to storahci key (msahci key was for Windows 7 and lower), is it there?

Here is the key.  What would you do with it?  I'm at a loss.
storahci-key.reg

Anthony:  Thanks!  That did it!

McKnife:  Thanks!  I saw your post after I'd done the regedit.  So, I undid the regedit out of curiosity and:
The right-click process did it.  Provide password to unlock initially, then select Auto Unlock.
The command line seemed to work as well .. reported it was already auto unlocking.  But appears to respond as one would expect.

So now it seems to be working without the regedit.  
And, now I don't know WHAT I saw that said it was an external drive.  It's not now.... It's a fixed data drive.
And, it's been through a cold boot.

The auto unlock feature will still detect it as an external drive if it already detected it like that, it will just automatically unlock it as long as no hardware/kernel changes were made to it's environment. That is the same way BitLocker treats an internal drive.

But with a question came two answers, so I guess pick your favorite.

Anthony:  It no longer detects it as an external drive....  But there's no explanation for why that would be.

Thanks all.

Thanks again!!