Default screen size on wptAgent

I have a few WPT agents running on a private instance of Webpagetest.

I updated two of these agents (highlighted), and they seem to be picking different screen sizes by default. Most of the other agents that are running on v18 have 1024x768 as their screen size. Can someone guide me as to where these agents might be picking these screen sizes by default?
Since the tests are sharded across all wpt agents, the tests that are run on these 2 machines seem to have a different screen resolution than the others. Thus adversely affecting my metrics.

I maintain the internal instance of webpagtest and multiple teams use this tool without supplying the screen size in their test configs. Hence its important that all agents maintain the same default screen size.

QLAB13 & QLAB14 machines run the following scripts for update :

@echo off
cd C:\Users\WebPageTest\browser-install
git pull origin release
python.exe C:\Users\WebPageTest\browser-install\ -vvvv --all
cd C:\Users\WebPageTest\wptagent
call npm i -g lighthouse
FOR /L %%x IN (1, 1, 24) DO (
git pull origin master
python.exe C:\Users\WebPageTest\wptagent\ -vvvv --server "" --location Location_ID --key Location_key --exit 60
shutdown /r /f

Continue to see a different screensize for these two machines even after upgrading all the wpt-agents to the same version.

Sharded tests that run on these two machines have very different SpeedIndex & Visual complete numbers because of bigger screensize.

Does anyone have suggestions why that might be the case ?