I'm getting constant "Galaxy Watch5 Manager Keeps Stopping" errors now too. Mine started out a week or two ago with the watch showing as "not connected" in the Galaxy Wearable app on the phone...even though the watch seemed to be connected and working okay. I tried resetting both devices, clearing cache, then clearing data, then resetting the watch to get it to show connected again. This happened three times when I finally uninstalled galaxy wearable, galaxy watch manager and factory resetting the watch itself. That's when I started getting persistent "Galaxy Watch5 Manager Keeps Stopping" messages and it's again showing "not connected" in the Galaxy Wearable app.
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