Got enough arena tickets to buy a Shadowstalker Torcine. Attached it to this wolf: https://www.lorwolf.com/Play/WolfDetails?id=187
This wolf is in my campaign party, but I cannot add the Shadowstalker to my party. After adding, if I go to save the party the party list instead disappears. If I refresh the page it does not show the companion as being added to my party.
This seems to be specific to this companion as I've switched to a different one on this specific wolf and it worked fine.