Olenka explained to me what you're asking. The problem is likely this:
1. You were at level 22.
2. Someone downgraded you to level 21.
3. You downgraded them to 21. The checkmark appeared.
At this point, their downgrade (from point 3) counted towards level 22 because you were at 21.
4. You upgraded back to level 22. The requirements are now reset.
When fulfilling requirements for 23, you need to be 22 (not 21).
So, what you were supposed to do instead is this:
1. You were at level 22.
2. Someone downgraded you to level 21.
3 (old 4). Upgrade back to 22.
4 (old 3). NOW downgrade the other Bastion to 21. The checkmark appears, but this time it is towards requirements for 23 (because you are now 22, not 21 like in the previous scenario).