Due to a bug in BE's mod-loading process, all mods which change unit promotions or build orders will cause the unit action bar to dissapear or appear garbled the first time you load them.
To work around this, when loading mods through the Mods screen:
1) tick the mods you want to use
2) click "next" and wait for it to say "configuring game data... please wait"
3) click "back"
4) click "next" again, and wait for it to say "configuring game data.. please wait" again.
The unit action bar should now display correctly when you start / load your game.