Can you provide more information, like the warning message and your setup?  Is the moblab running the tests or is it the test host in your setup.

This isn't a bug with the servos, it's that the mobmonitor check only looks for servo v2 USB VID/PID. So even if I had a servo v4 connected, the mobmonitor screen would always show "You don't have any servos connected"

I've provided a (not yet merged) fix here https://chromium-review.googlesource.com/c/chromiumos/platform/moblab/+/1044775

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform/moblab/+/ee7e403c268c72c7d641fe524c3fbe9588dac723

commit ee7e403c268c72c7d641fe524c3fbe9588dac723
Author: Matt Mallett <mattmallett@chromium.org>
Date: Thu May 10 22:10:05 2018

[moblab] mobmonitor check for connected servo v4

The ServoExists check does not detect a connected servo v4. Add the
servo v4 USB PID to the check.

BUG= chromium:839912 
TEST=test on local device. plug and unplug servo v4.

Change-Id: I726bc1f9f96780aff941c0d54f898acabf2e98b8
Reviewed-on: https://chromium-review.googlesource.com/1044775
Commit-Ready: Matt Mallett <mattmallett@chromium.org>
Tested-by: Matt Mallett <mattmallett@chromium.org>
Reviewed-by: Keith Haddow <haddowk@chromium.org>

[modify] https://crrev.com/ee7e403c268c72c7d641fe524c3fbe9588dac723/src/mobmonitor/checkfiles/moblab/servo_check.py