It could be heat. We see a lot more heat problems with the HBA cards in non server systems since they don’t have as much air flow or users turn the fans speed down because of too much noise. It could also be failing backplane, etc.
Can you check that all the fans are working or if you are getting any reported issues in IDRAC?
You can try following the Drive Troubleshooting in the Resources thread by @joeschmuck It may help.
