Hi Nigel,
In order to find the root cause of the issue, could you please provide the following information for troubleshooting?
1. Have you tried with another computer to reproduce this issue?
2. Did all the users with edit permissions in your organization run into this problem?
3. Could you edit the pages of a newly created site?
4. Could you capture a screen shot of the grayed buttons when you try to edit the page?
Thanks for your cooperation and support. I will be waiting for your updates.
Best regards,
Nancy Xie