For future testers who read this thread: I was able to successfully take Exams 1 + 2 online with no issues in Dec. I took Exam 3 online with no issue in Apr. When when I sat for my Exam 4 in Apr online, the proctor could not get my test to launch on screen. I spent 90 very tense minutes with tech support - on the phone in a noisy call center, via chat, and they even took control (with consent) of my computer at one point to try to troubleshoot.
I finally called CLARB when they ran out of options/my test was no longer available to take. I *highly* recommend anyone in the same boat do the same. A real person answered the phone right away, assured me I could retake the exam in 3 wks during their make-up window. I was sobbing honestly at that point - such high stress! I took the make-up test for Exam 4 this past Monday and feel pretty confident that I passed (results still to come).