I've been through the whole process again and I can now see (but not understand) the problem. The individual frames on the .gif look acceptable but the .gif itself is suspect. It was prepared using the timeline window of Photoshop CC release 20.0.7.
I'll re-run it again tomorrow morning and see if I can fix it.
If not I have CC release 2017.1.1 on the desktop - I'll try with that.
Hey, I'm always available to be of no help whatsoever.