Yes, I have an idea. It's because you're trying to do multiple crazy things with unsupported stuff. Stop trying to do those things.
What you are trying to do certainly sounds exciting for a lab host, but I doubt it is going to ever work reliable.
As the others already mention, you're in unsupported area.
The host isn't supported to start with, for vSphere 6.0 U3 the oldest supported HP 380 server is a Gen7, see also:
For the WiFi PCIe passthrough card, I don't even have to search if it is on the list as it is a desktop card, not server grade quality, so there's also no support for that.
In addition, OPNSense is based on FreeBSD. For FreeBSD, only version 9 and version 10 are supported on vSphere 6.0 U3. If you're running OPNSense 17.1 or newer then you are running against FreeBSD 11, which is .. unsupported.
I'm not even sure if PCIe passthrough is supposed to work on FreeBSD and this isn't even FreeBSD, so the guest OS that you are running is also unsupported.
As a result you are experimenting with a system that hasn't been guarantueed to work and the result you are seeing (the PSOD) isn't entirely unexpected.
I'm afraid that as a community there isn't much we can do at this moment, there are just too many variables at work here.
Hope this helps,
Wil| Author of Vimalin. The virtual machine Backup app for VMware Desktop Products
| Vimalin : Automated backups for VMware Fusion and VMware Workstation Professional
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Okay. I get it. No support for labs or something. thanks.