Issue with Storage Pool going offline - Server 2012 Standard

One of my clients are having an issue where their storage pool will go offline when data is being written to it or pulled from it. I can go in via disk management and turn the disk back online it comes back up just fine. This is just a standalone server that has 3 500GB SATA drives in a JBOD I believe. It has 1.36 TB total space. I do not think there are any other disks for redundancy. It's been years since we set this server up and haven't touched it since. After looking through the pool I noticed that it displays that it is out of free space. I thought this was odd because when I open up My Computer, it says there is 800GB of free space. After further review I noticed a rogue drive under disk management marked as disk 3. Disk 3 should be apart of the storage pool, but if you look in the first screen shot, it doesn't seem to be apart of it. In the second screen shot, you can see that PhysicalDisk3 is there. I think what happened was that disk got kicked out of the pool and it's causing the whole thing to fail. I appreciate any help you guys can give me! If there is any other info you need just let me know. Thanks so much!
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