"Unable to find the object Sys.Browser("chrome")" When Running Several Back to Back Tests

Two things to do - 

First, make sure that you are closing browser(s) at the end of each test run so that next time you start a browser, there's no confusion about which one is being used.

Second, use Wait Browser to make sure the browser is actually available before you begin a test.

https://support.smartbear.com/testcomplete/docs/reference/test-objects/members/sys/waitbrowser-method-sys-object.html