Mystical Kimchi

Honestly I have no experience with bitlocker since I don't use Windows much these days. I suppose it's possible that the decryption process didn't complete, and so some of the data is still encrypted. If it were my computer, and that happened to me, then I'd probably try turning bitlocker back on, then turn it off again so that I could ensure that the decryption process completed.

Okay, I found this on Microsoft's website:
So it would seem that, if bitlocker is working correctly, it probably resumed after your next reboot.
 
So again I'd suggest downloading and running a diagnostic tool to check the drive. Or even try running the checkdisk utility that comes with Windows. I'll even provide links to the download pages for utilities from the two most common brands of hard drives:
 
https://support.wdc.com/downloads.aspx?p=171&lang=en
 
https://www.seagate.com/support/downloads/seatools/

I had to follow up because I recently decided to give my DL380 G7 a good cleaning. I blew out all the dust with compressed air. I took cotton swabs with isopropyl alcohol and cleaned all 6 chassis fans thoroughly. Then, most importantly, I replaced the 10 year old thermal paste with Thermal Grizzly Kryonaut. I currently have all 12 cores pegged at 100% running xmrig and Folding@Home with Intel Turbo Boost enabled. The fans turned up a little bit, but not much. And CPU temps are hovering around 60 degrees Celsius. Before this cleaning and thermal paste upgrade, just having 2-4 cores at 100% with Intel Turbo Boost enabled would make this server sound like a jet engine. I had to disable Turbo Boost to prevent the fans from revving to 100%. Even then CPU temps would hover around 70 degrees Celsius.
 
Change your thermal paste. Use Thermal Grizzly Kryonaut. Trust me. You'll be astounded by the improvement.

Hopefully you'll get some good advice from people with first-hand experience. I recently had to shop for a low-profile graphics card for a Dell Optiplex 745. Being an older computer, I didn't see the point in getting anything high-end or expensive. I opted for an MSI Radeon R7 240. This was suitable for my needs, but it most certainly isn't what you need. I did a lot of Googling, reading articles and forum posts before I chose my card. This article https://graphicscardhub.com/best-low-profile-graphics-card/ was probably the one that was most helpful for me. But from looking online, the price range of low profile cards is pretty much under $200 or about $350.