Does Ubuntu 18.04 have problems recognizing two NVMe SSDs?

My server has two NVMe flash SSD drives. He had no problem using them with Ubuntu 16.04, but after reinstalling the server with Ubuntu 18.04, it only detects an NVMe drive. I changed the location of the slots of those two NVMe units, but the problem remained.

If I take out any of them, everything is fine. When I reinstalled the server with Ubuntu 16.04, it detected the two NVMe drives very well.

I wonder what happens to Ubuntu 16.04? I can not find any document that implies such an error.