pfsense 2.5.2 stops working in virtualbox

[routeigob]

I use pfsense for many years in my server. I have some virtual machines there in virtual box. All is working fine for many years, but now when I update from 2.4.5-p1 to 2.5.2 pfsense stop working. It works for some minutes but then ist stops. I try with 1 cpu core then it works but when I download something it goes to 100%, so one cpu ist too slow. All the years before 4 cores working perfect.

I try new install also . the same.
I try vmware workstation und esxi . It works. but that is no option for me. because when i use vmware with virtualbox together it crashes.

So can this be fixed that pfsense works with virtualbox????