When you say that all HP DL360 GEN9's are exactly the same and you are sure of that, then actually I would open a case with HPE as well. It could mean that even though hardware checks in ILO don't register anything odd, there still might be an underlaying problem under the hood there.
That being said, there are also two other things i would check.
- compare driver AND firmware versions of the hardware in your affected host with the working hosts and make sure they are all the same. Especially lpfc and network drivers.
- if you are usually do an in-place upgrade of your hosts instead of installing new images then sometimes legacy drivers might get in the way. This actually happened to us with qfle3 drivers where we had different results when running in-place upgrades or fresh install upgrades.
To do the above there are actually quite a lot of good articles around.
When it comes to HP I like to check the recipe and vib list of the custom image and compare that to what is actually in use on the host
Those pages also contain a lot of links if you want to dig deeper.
For checking your drivers there is this nice article (for 6.5, but still ok)
or just the kb
Not sure if this will help you in solving your issue, but hopefully it leads you in the right direction!
Good luck !