Had an issue over the past few weeks where I couldn’t swap out the root sharepoint site with a different site.

In the Office365 gui the error I got was  

Couldn’t replace root site …/sites/team Wait 10 minutes, and then try again

And in Powershell

> Invoke-SPOSiteSwap -SourceUrl https://XXXXX.sharepoint.com/sites/Team -TargetUrl https://XXXXX.sharepoint.com -ArchiveUrl https://XXXXX.sharepoint.com/sites/CommsArchive

Invoke-SPOSiteSwap : The operation is blocked due to maintenance. Please try again later

There’s a known issue that you need to enable the Office365 private CDN for this to work.  Command is below:

> Set-SPOTenantCdnEnabled -CdnType Private -Enable $true

WARNING: Enabling this feature will turn on a content delivery network (CDN) for this tenant to provide fast and

reliable performance for shared assets. The CDN may have privacy and compliance standards that differ from the

commitments and compliance boundaries outlined by the Microsoft Office365 Trust Center, and data cached through this

service may not conform to the Microsoft Data Processing Terms (DPT). For more information on CDNs,

see:https://go.microsoft.com/fwlink/?linkid=2077392

Confirm

Are you sure you want to perform this action?

Performing the operation “Enable Tenant CDN” on target “Private CDN”.

[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend  [?] Help (default is “Y”): y

WARNING: Files of type GIF,ICO,JPEG,JPG,JS,PNG,GLB stored in the locations configured to serve as Private CDN origins

will now also be served and cached in Content Delivery Network (CDN). Although only authenticated users are authorized

to access such content, the CDN is not monitored nor governed by Microsoft content policies.

After this, the site swap process just work