Unfortunately iOS 14 is unreliable. A few people have reported problems sending files from the phone to the watch. All but one of them were solved by rebooting both devices and trying again. However one person today had to resort to restoring his phone from a backup. This is Apple's recommended solution for one of their major bugs in iOS 14 (
https://support.apple.com/en-us/HT211865), so I am guessing this may be related.
This is obviously a major step so you may want to try unpairing and re-pairing the watch first, which Apple also recommend.
Sorry about this. As I say iOS 14 and watchOS 7 are unreliable. At any other time of the year I think Apple would have pulled such flaky releases, but that probably wasn't an option with the new watch hardware (which I am guessing cannot run watchOS 6 due to the lack of force touch).
It's not the fault of Apple's developers - they are put in a very difficult position by Apple's (very successful) culture of prioritising hardware over software. It seems that if the hardware is ready then the software has to ship, whatever state it is in. The same thing happens most years (and this year is actually not as bad as last year in my experience). Things usually stabilise eventually so hopefully they will bring out more stable versions soon.