OpenCL GPU Mining - 1st Card is underutilized, Why?

I have a CentOs 7 Ethereum Mining build that I use on several different mining rigs.

On certain motherboards, the "#1" card runs slower than the other cards.

It is not that the card performs worse, the card is only running at half-usage.

Of 5 different motherboards, 3 don't exhibit this and the other 2 are both stable but several generations apart.

Doesn't do it:

Asus Z270
Asus P8P67 LE
MSI Z-270-A Pro **

Does it:

MSI Z97 Gaming 5
Gigabyte "AOURUS" board

I've been able to confirm that the PCI Clockrates are the same, the PCI Bus Width & Speed is the same.

The CentOs distribution has ACPI and ASPM disabled. The distro is also "headless" so there is no X-Windows running.

It's gotta be something simple!

Here is the diff between the slow card and a "normal" card.

[root@frygrunt ~]# lspci -s 01:00.0 -vv > 1slo
[root@frygrunt ~]# lspci |grep VGA
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Fiji [Radeon R9 FURY / NANO Series] (rev c8)
04:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Fiji [Radeon R9 FURY / NANO Series] (rev c8)
05:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Fiji [Radeon R9 FURY / NANO Series] (rev c8)
06:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Fiji [Radeon R9 FURY / NANO Series] (rev ca)
[root@frygrunt ~]# lspci -s 04:00.0 -vv > 2no
[root@frygrunt ~]# diff 1slo 2no
1c1
< 01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Fiji [Radeon R9 FURY / NANO Series] (rev c8) (prog-if 00 [VGA controller])

---

> 04:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Fiji [Radeon R9 FURY / NANO Series] (rev c8) (prog-if 00 [VGA controller])
6,11c6,11
< Interrupt: pin A routed to IRQ 27
< Region 0: Memory at e0000000 (64-bit, prefetchable) [size=256M]
< Region 2: Memory at f0000000 (64-bit, prefetchable) [size=2M]
< Region 4: I/O ports at e000 [size=256]
< Region 5: Memory at f7e00000 (32-bit, non-prefetchable) [size=256K]
< Expansion ROM at f7e40000 [disabled] [size=128K]

---

> Interrupt: pin A routed to IRQ 28
> Region 0: Memory at c0000000 (64-bit, prefetchable) [size=256M]
> Region 2: Memory at d0000000 (64-bit, prefetchable) [size=2M]
> Region 4: I/O ports at c000 [size=256]
> Region 5: Memory at f7c00000 (32-bit, non-prefetchable) [size=256K]
> Expansion ROM at f7c40000 [disabled] [size=128K]
20c20
< RlxdOrd- ExtTag+ PhantFunc- AuxPwr- NoSnoop+

---

> RlxdOrd- ExtTag- PhantFunc- AuxPwr- NoSnoop+
27c27
< LnkSta: Speed 2.5GT/s, Width x1, TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt-

---

> LnkSta: Speed 5GT/s, Width x1, TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt-
33c33
< LnkSta2: Current De-emphasis Level: -3.5dB, EqualizationComplete-, EqualizationPhase1-

---

> LnkSta2: Current De-emphasis Level: -6dB, EqualizationComplete-, EqualizationPhase1-
36c36
< Address: 00000000fee0200c Data: 4122

---

> Address: 00000000fee0200c Data: 4142
[root@frygrunt ~]#

So it is the "Link Speed". But why? Nothing at all has changed except the Mobo.

** The MSI Z 270-A Pro doesn't have this problem but it is not suitable for mining.