I had the same issue, no Taptic on my watch just for alarms — and reported it to apple and they took my watch logs to see the issue.
However, I did read a fix for this and it works. Go to your alarms on your iPhone and set a new alarm with a ring tone AND a vibration (all of my previous alarms were set w no vibration before)
Now it’s fixed. You don’t even have to use THAT specific alarm ever or even set any other alarms with a vibration.
But now all alarms set on your phone or even directly on your watch will vibrate again.
Weird, huh?