Hey @neogenik
Have you used the TagInfo app, by NXP? I just read a flex One with it.
It might have to do with the shape of your antenna on your phone. Most often it’s just getting the position right. Here is a picture with the shape of the Galaxy S10 NFC antenna depicted. Try laying the flex One parallel and perpendicular to the rectangle.
Is the tag implanted, or is it still inside the vial with the chlorhexidine?