Periodical interrupt storm when playing game with USB keyboard

Hi

Finally I found the root to the problem that's been having me puzzled for
the last week.

I started playing UT2004 on my laptop while away from home. Worked
perfectly. When I'm home and connect external display+mouse/keyboard, I get
weird random lag.

It is intr process that goes up to 100% CPU usage (swi4: clock) for a
couple of seconds every 30 seconds or so, but only when I'm moving around
in the game. To move around you need to hold down any of the wasd-keys.

Turns out, the interrupt storms only happen when I use my external
keyboard, not with the laptop keyboard.

The internal keyboard is:
atkbdc0: <Keyboard controller (i8042)> port 0x60,0x64 irq 1 on acpi0
atkbd0: <AT Keyboard> irq 1 on atkbdc0

and external (Microsoft sculpt ergonomic desktop):
ugen0.2: <Microsoft Microsoft 2.4GHz Transceiver v9.0> at usbus0
ukbd0: <Microsoft Microsoft 2.4GHz Transceiver v9.0, class 0/0, rev
2.00/7.97, addr 1> on usbus0

The game runs with a linux binary. 32/64bit both act the same.
It uses libSDL-1.2 from /compat/linux/lib for rendering but not sure about
input events.

I tried lowering the key repeat rate both with xset and kbdcontrol but it
has no effect.

I don't have any wired USB keyboard to try with.

Anyone have a clue to what's going on?

Hardware is Dell Latitude E7270
with
FreeBSD 12-CURRENT
drm-next-kmod
linux-c6