On International flights to Europe, Comfort+ still works the "old" way - assigned at booking without an upgrade wait list or different fare class. That could be causing weird IT issues as they update the web site. I know I've seen ads to upgrade to Comfort+ for $0 inappropriately on both the app and web site, sometimes even after an upgrade certificate to business class has been applied, so I wouldn't worry about that aspect of it.

I'd recommend watching the trip closely to make sure your seat assignments stick - as these routes too transition to upgrade processing, your tickets should automatically get updated without any action on your part, but it never hurts to be vigilant. I recommend once a week until departure or so, ideally on mondays after the weekend schedule changes have processed.

Note that Comfort+ paid seats come with zone Sky boarding, but not other SkyPriority services (priority checkin/security lines/customer support). That could explain the lack of a tag on the reservation. If you have an elite level and expected SkyPriority access based on that, make sure your frequent flier number and status are properly reflected in the reservation. Otherwise, your boarding passes should print with SKY zone, but will not reflect SkyPriority and you should expect to use the general checkin and security lanes.