Faced the same issue today, 7 Nov 2021, as well.
In the beginning, when connecting to the proctor, their conferencing system was not very good. The sound of the proctor was echoing and the proctor couldn't hear me. They thought it was my internet's problem, but it was not. In the end they told me to use zoom instead, so I moved to zoom. It was so much better - we could hear each other clearly. The proctor tried to set-up the exam but couldn't put in the right passkey for quite a while. The proctor eventually managed to get the right key and so could get the exam started. This whole set-up took 45 mins though, instead of the estimated 15 mins.
The exam began, and the whole system was very very veryyyyyyyy laggy. For instance, I took the verbal section first and in the first question, I couldnt click on anything for 5 minutes. Then same thing happened for the next question. Took me 10 minutes to get through the first 2 questions. Tried calling the proctor, but no one was there. From that point (2 questions into the exam), I knew it was going to be a very long and tiring exam. After the 2 questions, the system improved a bit (didnt take me 5 minutes to click on anything), but the next button was still very slow. Took 30s or so to go to the next question every time, and this was deducted from the overall clock. So lost a lot of time on this. Tried to speed up and catch up in the later part of the section. But towards the end, the browser suddenly shutdown on its own. The proctor had to restart it. Again, lost a lot of time on that and in the end the section ran out of time.
The first section was already so mentally draining because of the whole lag. I asked the proctor what's wrong and if they could help fix it. However, the proctor was just continuing to read off a script and asking if I wanted to take a break or not (hellooo...priorities!!!) I told the proctor that you are not answering my question and addressing my issue at all. In the end, the proctor told me to contact GMAT about the error instead. So at that point was really frustrated already, knowing that I had to endure another 2 hrs worth of super lagging system that will obvs lead to unoptimal outcomes.
The subsequent sections (Quant and IR) I just had to endure the lag. Not any better at all.
The AWA section was slightly better because didn't have to click next. But the text typing was not very real time either. Was also lagging. But at least i didn't have to endure a few more lagging next buttons.
Anyways, have reported this to GMAT. Hopefully they reply with some sort of compensation! It's really unfair. If I were to retake the gmat, would prefer to do it offline.