Thanks for the sysdiagnose pointer (this should be added to the documentation page). I found this:
Service: applinks
App ID: TeamId.bundle.id
App Version: 510.0
App PI: <LSPersistentIdentifier 0x104622ac0> { v = 0, t = 0x8, u = 0x8a4, db = 284B9176-578F-42D3-A1D7-9F82DA98D040, {length = 8, bytes = 0xa408000000000000} }
Domain: mydomain.com
User Approval: unspecified
Site/Fmwk Approval: unspecified
Flags:
Last Checked: 2022-01-27 20:20:37 +0000
Next Check: 2022-01-27 23:55:10 +0000
Error: Error Domain=SWCErrorDomain Code=7 "SWCERR00101 Bad HTTP Response: 503 Service Unavailable -- {"status":"503 Service Temporarily Unavailable"}" UserInfo={Line=274, Function=-[SWCDownloader URLSession:dataTask:didReceiveResponse:completionHandler:], NSDebugDescription=SWCERR00101 Bad HTTP Response: 503 Service Unavailable -- {"status":"503 Service Temporarily Unavailable"}, UnderlyingError=Error Domain=HTTP Code=404 "(null)" UserInfo={Line=274, Function=-[SWCDownloader URLSession:dataTask:didReceiveResponse:completionHandler:]}}
Retries: 1
This 503 error could be because of geo-restrictions on the site itself, I'll try to fix/check this with sysadmins.