S4048-ON switch unsupported QSFP+ cables

I have a VLT setup from 2 x S4048-ON switches (identical firmware, bootflash, bootselector, CPLD) and have all of the 10G ports used and everything seems fine. However, I tried using a few QSFP+ cables on available ports to gain additional split 10G ports and encountered a weird issue where these ports will be flagged as either "Media not present or accessible", or they are marked as "dell qualified = no" or "dell qualified = yes". If they are not marked as dell qualified they have a very unstable connection on pxe boots and so on (even though they work perfectly fine on other models of dell). 

When plugged into working VLT switch:

Slot Port Type Media Serial Number Dell Qualified
-----------------------------------------------------------------------------------

1 49/1 Media not present or accessible
1 49/2 Media not present or accessible
1 49/3 Media not present or accessible
1 49/4 Media not present or accessible
1 50/1 Media not present or accessible
1 50/2 Media not present or accessible
1 50/3 Media not present or accessible
1 50/4 Media not present or accessible

and sometimes:

Slot Port Type Media Serial Number Dell Qualified
-----------------------------------------------------------------------------------

1 49/1 QSFP 40GBASE-CR4 INS315673 No
1 49/2 QSFP 40GBASE-CR4 INS315673 No
1 49/3 QSFP 40GBASE-CR4 INS315673 No
1 49/4 QSFP 40GBASE-CR4 INS315673 No
1 50/1 Media not present or accessible
1 50/2 Media not present or accessible
1 50/3 Media not present or accessible
1 50/4 Media not present or accessible

 

If I unplug VLT peer link and uplink (both 40G ports) and then plug in QFSP+ cables first:

Slot Port Type Media Serial Number Dell Qualified
-----------------------------------------------------------------------------------

1 49/1 QSFP 40GBASE-SR4 MSY5AV30040 Yes
1 49/2 QSFP 40GBASE-SR4 MSY5AV30040 Yes
1 49/3 QSFP 40GBASE-SR4 MSY5AV30040 Yes
1 49/4 QSFP 40GBASE-SR4 MSY5AV30040 Yes
1 50/1 QSFP 40GBASE-SR4 MSY5AV20035 Yes
1 50/2 QSFP 40GBASE-SR4 MSY5AV20035 Yes
1 50/3 QSFP 40GBASE-SR4 MSY5AV20035 Yes
1 50/4 QSFP 40GBASE-SR4 MSY5AV20035 Yes

 

Does it suddenly become dell qualified? Is there perhaps a known reason? I can't have something unstable like that, especially during reloads.

 

#show system stack-unit 1 (some info is removed with '#')

-- Unit 1 --
Unit Type : Management Unit
Status : online
Next Boot : online
Required Type : S4048-ON - 54-port TE/FG (SK-ON)
Current Type : S4048-ON - 54-port TE/FG (SK-ON)
Master priority : 0
Hardware Rev : 2.0
Num Ports : 72
Up Time : 1 wk, 1 day, 0 hr, 28 min
Dell Networking OS Version : 9.11(2.1)
Jumbo Capable : yes
POE Capable : no
FIPS Mode : disabled
Boot Flash : 3.21.2.6
Boot Selector : 3.21.0.0-5
Memory Size : 3201302528 bytes
Temperature : 38C
Voltage : ok
Serial Number : NA
Part Number : 0TF3V9 Rev A01
Vendor Id : DL
Date Code : 15102016
Country Code : CN
Piece Part ID : #
PPID Revision : A01
Service Tag : #
Expr Svc Code : #
Auto Reboot : enabled
Burned In MAC : #
No Of MACs : 3

#show revision

-- Stack unit 1 --
S4048-ON SYSTEM CPLD : 15.2
S4048-ON MASTER CPLD : 12
S4048-ON SLAVE CPLD : 5