I am facing this issue inside our sharepoint online root site collection:- when i tried to add some custom properties to our modern site pages, by going to Site Setting >> Site Content Types >> i click on the built-in "Site Page" content type. Where i thought i will have the options to add some custom columns to our "Site Page" content type, but i found that the content type does not have any options under the Settings + there is not option to add columns to the content type, as follow:-

enter image description here

while if i create a new site collection let say @ https://ourcompanyname.sharepoint.com/sites/siteA , then the "Site Page" Content type will have "Advance Setting" link under the Setting + will have options to add columns to the content type ("Add from existing site columns" link), so i were able to add cusotm properties to it, as follow:-

enter image description here

so is my issue only happen at the root site collection? and how i can fix this?


The reason is the content type "Site Page" at "/" is sealed. I don't suggest you modify it, if you still want to add custom columns to this content type, try to use PnP PowerShell to achieve it.

$credential = Get-Credential  
Connect-PnPOnline -Url https://xxx.sharepoint.com/ -Credential $credential
$ctype = Get-PnpContentType "Site Page"
$ctype.Sealed = $false
  • thanks for the reply.. But is it a supported/recommended approach to unseal the built-in “Site Page” content type inside our root site collection? And if it is a supported operation then why this content type is set to be sealed by default? Keeping in mind if I create new site collection (also of type classic team site) the “Site Page” content type will be unsealed by default.. so seems my issue is only happening on the root site collection? – John John Nov 13 '18 at 12:04
  • 1
    This is by default for root site collection, it is not recommended to unseal it. As a workaround, you can create a new site collection. – LZ_MSFT Nov 14 '18 at 1:26
  • thanks for the reply. I can not create a new site collection, as i already have many pages & sub-sites already created at the root site collection. second point , i can not get my mind why it is not recommended to unseal the "Site Page" content type on the root, while creating a new site collection will make it as un-sealed by defualt. third point, i can see that there might be a risk of unsealing a built-in content type. .. – John John Nov 14 '18 at 2:04
  • but i do not have to create a new site collection, i can add a custom content type which inherit from the built-in "Site Page" content type and define the custom CT as the default CT for our "Site Pages" library, will this be a supported appraoch? can you please advice on these 3 points? – John John Nov 14 '18 at 2:04
  • Yes, create a custom content type which inherit from the default "Site Page" content type is a good idea. You can do it. – LZ_MSFT Nov 14 '18 at 2:26

It looks like the update that "fixed" this issue (ie unsealed the site page content type) only works on sites created after the update was applied to your tenant. Msft seems totally unaware of this and oblivious to the problems and confusion it causes for the majority of their customers with pre-update sites. Run the powershell unseal script above in an affected site and it should fix the problem. I would also contact Msft via service request and ask that they confirm this is the cause and come up with a supported, tenant wide solution.

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