OK, this is baffling.
I have a Cavium / Brocade / Qlogic 16Gb / 10GbE FCoE CNA Network HBA (BR0110401-38 / RS-1860-2A01).
It has two SFP+ ports and is configured for FCoE, which means it shows as 4 devices (2 NIC and 2 FC) but when I attempt to select one in Host->Manage->Hardware->PCI Devices in order to toggle PCI passthrough, the 4 devices start randomly auto-selecting and deselecting... by themselves! It's like an animation - see the attached .mp4 which I took on my phone.
This occurs on both my hosts (ESXi 6.7U3 on a Supermicro machine, and ESXi 7.0 on a Dell R730) when accessed using Firefox, Chrome or Opera browsers running on Windows 7 & 2012R2 on three different machines.
I've updated the firmware on the HBA to the latest version, as well as all the BIOS/Firmware on the SuperMicro & Dell.
Anyone else come across anything like this???