I have the same issue with my iPhone 11pro and Apple Watch 6 ( all up to date).
Trying to solve it with apple technical support for more than one month now (sent several diagnostics, multiple phone calls).
The only solution when the watch is no longer ringing : restart the iPhone ... or start and stop my car (BMW 3Series June 2020) with CarPlay for few minutes. Also as mentioned all other devices (iPad and MacBook, IMac ) do not ring either, so impossible to have a call at the office on iMac
david197602
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