I am running a custom build AP with 3x Z-Com Xi-626 PCI wifi cards. Those are rather old cards based on Intersil Prism 2.5 chipset. The machine used to run old 2.4 series kernel with out-of-kernel hostap module and the machine was running flawlessly for several years.

Recently, I decided to do a complete system update and tried to compile the latest kernel 5.1.3 with hostap_pci build as module. The cards are detected correctly and everything works until I try to bring them up. At that point the machine completely freezes and only a "SW TICK stuck" error is printed repeatedly to the console.

I tried different kernels and actually found out, that the kernels prior to 5.0 seems to work. Right now I am running 4.19.44 and I did not experience this problem.

Can anyone verify, that the hostap suffers problems in latest 5.X kernels?

A good thing to do would be to report the bug upstream in the kernel. The maintainer of the driver should be interested. With different version of the kernel you should probably have a kernel log that would allow to make a valuable report. If you need assistance on how to do it, let us know.