Dell R530 Slot Empty issue

I have an issue with expanding storage in our Dell R530 Servers. We have three of them.

When we bought them they had 4 SSDs and 4 HDDs installed each. HDDs are 400-AEGK-56 (4 TB SATA). Recently we bought 2 more HDDs (also 400-AEGK-56) and replaced 2 SSDs with HDDs in every server in order to expand storage. Together with HDDs we got KG1CH-14 [ 3.5" SAS/SATA Hdd Tray Caddy for PowerEdge 13G. Compatible with PowerVault MD1200 PowerVault MD1400 PowerVault MD3200i ] 

New HDDs were added trough iDRAC.

The problem is that after some time iDRAC issued slot empty for every one of those drivers, after server restart they reappeared and were successfully added to our ceph storage. Afterwards we noticed they were missing again within iDRAC (although they are added to our storage without any issues and we can see them in our storage pool). One of our servers is reporting slot empty only for one HDD, and two servers are reporting slot empty for both drive bays which were upgraded...

Also we got these log errors:

ENC26: Integrated RAID Controller 1 is not responding, Detailed description: The enclosure or an enclosure component is in failed or degraded state. It is not responding to storage management commands or there is a connectivity problem between the controller and enclosure.

Also ENC 24: Communication with integrated RAID controller 1 is intermittent, Detailed description: The controller is not receiving a consistent response from the enclosure. There could be a firmware problem or an invalid cabling configuration. If the cables are too long they degrade the signal.

What course of action do you recommend us to do?

Thank you in advance for your help.