One thing that I had overlooked amonst all of the settings was the "Notifications->Notification advanced settings->Notification access" area of my Droid (OnePlus2) settings whereby you can allow apps to access to your notifications. Make sure "Galaxy Wearable" is enabled there. Somehow I think this got altered during my Galaxy watch software/firmware update.
I had this same problem and could not figure it out for weeks. I just realized that my do not disturb function was turned on for some reason (duhh). So if you have tried literally everything, maybe check that?? Wish I could be of more help.
I have followed these steps and it did fix my problem for about 3 hours. By the end of the day I was once again not receiving text notifications but everything else was working. I'm getting close to returning my watch.
So I found this thread trying to figure out why I would get messages for everything other than text messages from my iPhone X. I read a lot of the comments and if someone posted this and I missed it, sorry in advanace, but it seems you need to go to the Notifications on your iPhone and turn Show Previews to Always. That was all it took. I read one post that said only worked in vibrate mode but mine is working now in any mode. Hope this helps! It only took me 2 hours to figure this out and I was 5 minutes from sending this watch back. Now, to see if I enjoy really enjoy this smartwatch over my Apple Watch.