Makers were reporting that they were getting intermittent upstream connect error or disconnect/reset before headers reset reason: connection termination errors in their PWAs after publishing a new build. And when the app loads successfully, list loading is noticeably slow.
This is fixed today by the engineering team (Also a senior engineer mentioned that with the fix, web apps should load faster now too 
) and if you’re still experiencing a similar issue, please submit a support ticket or create a new thread on the forum!