I have an iPhone X and Apple Watch 5 with no issues at all. Unfortunately, I also have an iPhone XS and Apple Watch 5 combination with Bluetooth communication issues and resulting is extremely rapid battery discharge on both devices. Have tried disable/enable of Bluetooth, rebooting, power off/on both the iPhone and Apple Watch without success.
Has anyone tried the un-pair/re-pair option?
UPDATE: Have found that entering Airplane mode on the watch with both Wi-Fi and Bluetooth disabled reduces the battery drain. On the watch be certain to turn off the Mirror iPhone option or you will lose all Bluetooth connections. Options may be found at General/Airplane Mode/Mirror iPhone.