Been wanting to know what this means for a while now. I gave Juliet a gift when instead of a heart icon on the button to give her the gift there was a green circle. After that the circle turned yellow and there was no green check. It's been several days since I gave her the gift and the yellow circle is still there. Am I doing something wrong?
Have you completed her storyline? Or are you still progressing with her? When you gave her the gift, did you do story content?
The green circle means the character bond is very close to reaching 100%, (you'll need 100% to progress to the next chapter) so green would be like 80%+. Green check means you've given a gift already for the day.
Yellow circle would be the bond is somewhere in the middle, 50% give or take. The symbols go Black > Red > Yellow > Green > Heart.
If you had given her the gift when it was green and you did story content, it means that the gift you gave was enough to reach 100% and you'd have gone through the chapter and then it would reset to the next stage.
It might be a bug if you've completed her storyline as gifting is no longer required for that character and that bond tracker doesn't know what to do.