Errors caused by our proxy do show up in logs. They look like:
2021-06-30T00:22:34.487955794Z proxy lhr [error] error.code=1002 error.message="No suitable (healthy) instance found to handle request" request.method="HEAD" request.url="/admin/signin" request.id="01F9D4NTQM2PJX6XF2SW08A786" response.status=502
(this was taken from one of your other posts: 502 errors from app ... possibly related to 525? 
)
If there are none present, then our proxy has not produced it. Or the log got lost somewhere in transit (but I haven’t heard of such reports).
We don’t log all HTTP requests because this would mean and extra hundreds of millions of log lines per day.
If you don’t mind sending me your app name, I can take a closer look.