What does Bia rank 4 do?

Mine does not display green upgrade text for any stat and “movement speed” doesn’t display a percent at all (not even the current) when I check the upgrade results screen. 

It’s supposed to increase your troops’ movement speed by another +5%. We already noticed that it currently doesn’t though and it will be fixed in the next server update.

I’ve noticed this too so haven’t bothered with it yet

This is also the case upgrading guard of Thanatos to level 8 it doesnt show any improvement 

Upgrading the Guard of Thanatos to level 8 and beyond increases the maximum level of your defense waves. It allows you to upgrade each wave to a new level which increases their morale.

It just doesn’t give you a new wave because you cannot have more than 7 waves.