G-SPEED Studio R Write Speed Super Slow

I used to depend on this storage as a reliable fast source for my media while editing, but lately I’ve noticed it’s really been chugging along, so I ran some disk speed tests using AJA and Black Magic, and both showed that my write speeds are just under 100 MB/s, and the read speeds aren’t a lot better, at 380 MB/s.
I used to be up over 700 MB/s read and write.
What’s happened?
The 24TB of storage is configured as RAID 5, giving me about 18TB of storage to work with. I’m currently only using about 9TB of that space.
I’m running macOS Big Sur, 11.2.3
Could it be Big Sur?
Do I need to “optimize” the storage somehow to get the speeds back up?