I know it is an early developer beta, and I haven't even begun to debug it, but Slack running in this method does not perform well. My sent messages frequently show and then get stuck in the grey "sending" text indefinitely after they appear as sent on other devices, and I often don't receive messages in the web app until I force a refresh.
This is my experience with Slack as a PWA in Chrome, or even in a regular tab in Safari. My guess is that Slack doesn't play nice with attempts to snooze background tabs to save system resources.
I know it is an early developer beta, and I haven't even begun to debug it, but Slack running in this method does not perform well. My sent messages frequently show and then get stuck in the grey "sending" text indefinitely after they appear as sent on other devices, and I often don't receive messages in the web app until I force a refresh.