I've tried switching the NVMe slots as well with the same result. Pulling the new NVMe drive allows my system to boot back up normally.

Just check to see if the BIOS is set to RAID. If it is then you could try switching it to AHCI. It really shouldn't matter if it was set on RAID but it's possible that it's causing an issue. 

Is there an OS already on the newly installed drive, or is it blank?

There's not an OS on the new drive but there is on the other m.2 drive that was already installed prior to this. The drive with the OS has not been removed.

In the online m15 R1 Setup and Specifications article, I do not see any three drive configurations nor do I see 4TB.

According to this post having 3 drives is ok as long as you don't have the big battery, which I don't.

According to this post and many others on the web 4tb NVMe drives and even higher capacities will work just fine.

As I mentioned, I can see the drives listed and read correctly in the BIOS. You would think that would not be the case if it were merely a compatibility issue with how many drives are connected or how big one of them were.

It sounds like it has something to do with how the system has the drives set up. It seems like it's trying to use both NVMe drives in RAID but since there's no Windows image on the new drive then it can't work it out. Did you try looking to see if it's set to AHCI or RAID?

Yeah, if the drives aren't set up for RAID then it really shouldn't make a difference what the BIOS is set to. Something isn't right though if the system is having issues when the extra drive is installed. 

Usually switching to AHCI shouldn't cause any data loss since your drives aren't set up in RAID but I'm not going to put my house on it since it's your laptop. The only time you should have an issue is when you are in RAID0 and try switching. 

I've had a few issues before with the 17 R1 which often had a small cache mSata drive which would be used to accelerate a large mechanical HDD using RAID. Sometimes removing the mSata and trying to just run off a 2.5" drive would cause some strange issues until I switched the BIOS to AHCI. 

Yes it does appear to be set to RAID. Take a look at the pics of my BIOS in the links below to confirm. It's giving me a warning about potential data loss if I change it so I just want someone to confirm it should be OK. The drives don't appear to be RAID configured so I don't see it being an issue but I'd feel better with confirmation.

https://ibb.co/2h5RZsQ
https://ibb.co/QmsNttw
https://ibb.co/yqhSMWW

Totally agree, not really concerned about it being a problem, just wanted another set of eyes on it to make sure I'm not having a massive brain fart. Being cautious is all.

I'm going to throw the drive back in amd change it to see if it makes a difference.