Why won't it let me start a streak pet with a specific friend?

Title is self explanatory. It won't let me start a streak pet with one of my friends (which is ironic bcz he's the friend I talk to most on TikTok) but it will with other friends. The button is there to start one on 3 out of 5 of my streaks, the other two don't have the button. How do I fix this? It won't let him start one either