Why are my iPhone and Apple Watch notifications out of sync after updating to iOS 18.1?

Did you try to force restart your watch and iPhone after the latest updates?

To force restart, hold down the Digital Crown and the Side button at the same time for at least 10sec, until the Apple Logo comes back again on the screen.

Force restart iPhone - Apple Support

The next step would be unpairing the watch and connecting it again to your iPhone:

Unpair and erase your Apple Watch - Apple Support

If this does not work, you should let Apple know directly about this issue by using the Feedback link, as this is the only way to reach them.

Feedback - Apple Watch - Apple

Feedback - iPhone - Apple

Since I switched to ios 18.1 & watchos 11.1, I've been having similar problems. Notifications of incoming calls sometimes don't appear on the apple watch, and incoming imessage or whatsapp notifications only appear and can only be read after tapping the screen of the apple watch. When this is not done, I only get vibrations on apple watch. Tried forced restart on both devices.