ISATAP on 2019 Direct Access Server doesn't work

Try to build an easy "Direct Access Manage Out" solution for accessing connected DA clients, according https://directaccess.richardhicks.com/2013/06/24/isatap-recommendations-for-directaccess-deployments/ and other guides. Have done that before on earlier server versions, and it worked from the start.

But on server 2019, there seems to be a problem with the ISATAP router. 

• get-NetIsatapConfiguration tells me that the ISATAP router is enabled
• netsh interface ipv6 show interface shows two connected ISATAP interfaces: One with the name "isatap.domain.local", the other with the name "isatap.{GUID}". The GUID corresponds to the GUID of the Interface of the internal NIC of the DA server.
• But despite all that, the ISATAP interface with the name "isatap.domain.local" has no IPv6 address (except the link local address). 
  
  

Have examined the same on a working 2012 R2 direct access server. The very same interface has a valid IPv6 address assigned:

Any advice? Thank you in advance for any help.

Franz