Hi!
We just had a similar case at https://forum.fairphone.com/t/ubuntu-touch-with-threema-on-anbox-where-are-the-files/53768/12 , a fairphone 2 running the stable channel. After changing to rc channel Anbox installation, that was stuck like in this case, could be completed, and now works. Perhaps you could give it a try? (if you are on stable, nobody knows but you...).
But you left the forum; so we'll never know. I hope it helps in other cases.