Hello JasonR
I understand that you are facing connectivity issues because your VPN Gateway’s address pool has unexpectedly changed.
I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this!
Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others", I'll repost your solution.
Please click "Accept" the answer as original posters help the community find answers faster by identifying the correct answer.
Issue: Virtual Network Gateway missing address pool
Resolution:
Your VPN Gateway address pool has been changed. After adding the correct address pool, your issue has been resolved. Please add your troubleshooting steps in the comment section to assist other community members.
Please don’t forget to close the thread by clicking "Accept the answer" wherever the information provided helps you, as this can be beneficial to other community members.
Please do not forget to "Accept the answer” and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.
If you have any other questions or are still running into more issues, let me know in the "comments" and I would be happy to help you.