RAID 1 works until it doesn't on D5-300C

[js2442]

I have repeated this several times now. I configure drives 1 & 2 for RAID 1 and the rest as individual drives. All are 4 TB drives. Everything looks correct and works fine for an hour or two. I can copy data to any of the drives. Then suddenly for no apparent reason the drives in the RAID 1 group show as uninitialized and sometimes a third drive shows as uninitialized. I say "sometimes" because, and this is even more unsettling, the Windows partition manager does not show the same partition table as a third party partition manager Active@Partion Manager. This PC has had various external drives attached for many months and never exhibited any problems at all with partition tables.

Additional info: drives 1 and 2 are the exact same model, drives 3, 4, and 5 are all 4TB but different manufacturers. All drives have a history of normal operation and all were tested with a diagnostic app before install.

Any ideas? I'm going to try operating with just the 2 RAID drives to see if the variety of drives is triggering shall we say less than robust drivers although I'm not sure what good that will do because if I wanted to spend money on all new identical drives I would probably upgrade to a Synology NAS making this a moot point. Was hoping to repurpose some old drives I had available.

Thanks in advance for any help.