Lower the time tests are allowed to queue before we time them out to under a minute. We consider it an antipattern for customers to queue multiple tests, yet by default we let them do it for about 10 minutes. Customers could specifically opt into a longer queuing time; making it clear they've asked to violate best practise.
Change the error message to reflect that the users test runner cancelled the browser request, not Sauce Labs.
Either through popup or email, notify customers that their trying to run too many tests and it's freaking their test runner out.
Customers without queuing problems will be unaffected.
New Customers with queuing problems will discover them more easily and have a more satisfying onboarding experience.
Existing Customers with queuing problems will start to have more test errors until they stop over-queuing.
Existing suites with substantial queuing will start to fail.
Customers who don't want to manage their own concurrency will get even madder. This is an occasional complaint, despite concurrency limits not changing that often.