Had the same problem, cache rebuild solved it.
The solution in #4 works, but I had to do it as suggested in #7 - delete originally created migration field, which was a single date.. create new fild with same name, but daterange. run customized import again and it worked. D6 -> D9
So far this works in Seven theme. When menu is created, links are replaced correctly in Seven (admin) theme. Even if I put menu block in theme seven, links are generated properly. In Bartik and any subthemes, links are rendered as token text - as they were input in form.
[deleted, thought I found a solution, but didn't]
I solved this by updating to latest dev AND creating new menu + links. Something seemed stuck in previous menu and tokens were used sporadically.. sometimes yes, sometimes not.