This is the scenario that I have mentioned before that I have only noticed when my phone is face up and I see it happen.
My Galaxy Watch 4 never even notices it happening and I never receive a "disconnect" notification.
What you are experiencing is a system server reset. Your android framework is crashing and rebooting itself to restore functionality. Please try the below.
[Settings] → [Applications] → [Menu] → [Special access] → [Optimize battery usage]
→ Change the filter (upper left corner) to "All"
→ Find the browser related apps, and change the option from "ON" to "OFF" to exclude the app from "Battery optimize target"
One UI Beta Team
And I did a global search in Settings - Optimize Battery Usage does not exist in Settings, for me