Created a new test user and tried to make edits again, didn’t work. Must be on newly created users.
From the error message it looks like this issue is related to folder permissions. Try opening the folder properties editor (the gear icon in the upper right of the dashboard, you will need to click on the folder once first) on the folder that contains this page. Expand “Permissions” and ensure that the newly created users are granted “write” access to this folder.
Were you able to test based on John’s reply?