APC SMT3000I - resistor R11 (0R33 5W) smoking

Hello,
I have two APC SMT3000I which both have the same problem.
https://www.apc.com/shop/de/de/products/APC-Smart-UPS-3000-VA-LCD-230-V/P-SMT3000I

If you turn on the UPS and it performs a self-test it can happen that 
the load resistor R11 - 0,33Ohm, 5Watt (Only once on the board) starts 
to smoke and then burn out.
This can also happen when switching to battery operation.

The probability that the resistance smokes during the self-test is about 
50%. If the UPS passes this, the probability is again at about 50% when 
switching to battery operation with the same problem. The UPS produces 
then a very unhealthy "screaming" noise (see video).

I have already replaced the resistors of both UPSs several times after 
they were completely blown out. The error message on the display then 
showed "Overvoltage at the output".
As described, it can happen that the UPS easily pass the test and also 
run smoothly on battery, without the resistance burns through. (Battery 
calibration has gone through recently without problems)

I have the assumption that in both scenarios the power from the 
batteries is sent somewhere wrong through the board, and produces a 
short circuit within the board. (Relay not switched ?!)

Here is a video with new batteries, 100% charged (self-test passed, even 
with smoking resistor). : /
You can hear how the power can not even be maintained for 250W and the 
hot air gun is weakening. After 20 seconds, the battery was at 55%.
https://youtu.be/y2zbfGiP5Fg

I would be very grateful for any idea.
Greetings Florian