Apple Watch alarm haptics intermittently

Every night I place my iPhone 17 Pro on to my charging dock and wear my Apple Watch 10 on my wrist. My phone and watch is set to sleep mode and do not disturb and the devices are up to date. My alarm is set through sleep schedule.

Most of the time I get woken up by the haptics on my watch but every now and then the haptics don’t work in my watch. The screen on both my watch and phone has the alarm screen on, indicating the alarm has triggered.

How do I ensure this works every time?