Hi @mingoo , It’s an odd one. 😕 I don’t have a Galaxy Watch4, but the only way I could come close to replicating the same issue with a UK S10 and a Galaxy Watch 3 was by disconnecting the two devices and trying it when out of Bluetooth range.
If you haven’t tried it already, you could try unpairing and re-pairing (on your S10: Settings > Connections > Bluetooth > [tap the cogwheel next to the device you want to unpair] > Unpair).
Might also be worth sending an error report with log files and a screenshot/short video of the issue via the Wearable app. Guide on how to do that here: https://eu.community.samsung.com/t5/wearables/galaxy-wearables-how-to-send-error-reports-for-galaxy/...
