Run the check
Test each suspect key slowly, then repeat the same sequence quickly.
Compare one key alone with the troublesome combination.
Repeat in a text editor and check the existing rollover guide for combos.
Read the result
Only fast combinations failing suggests rollover or app input handling.
Limits and next step
Browser events do not measure the moment a finger actuates the switch.
Repeat the check after changing one setting or connection. Keep a record of what changed before deciding whether the device needs service.