Running Three Test Suites in Parallel, Third Suite Fails All TCs

attention

#1

Note: Despite my use of the term “in parallel” below, THIS IS NOT ABOUT COLLECTIONS.

I have three test suites, S1, S2, S3.

I can run all three of them sequentially without any issue.

I can run any two of them by hand, in parallel, (click Run, click Run) without issue.

In any order, I cannot run three by hand, in parallel. The third will always fail every Test Case with the same error:

Test Cases/Pages/Sample/Test blah blah FAILED.
Reason:
com.kms.katalon.core.exception.StepFailedException: Unable to execute JavaScript.

Caused by: …BrowserNotOpenedException: Browser is not opened

I tried to create a Suite Collection set to execute in parallel, but same issue, the last suite in the list fails with the same errors.

OS: Win10
Browser: Firefox/geckodriver