Max level companions are marked as a candidate to level up:

This broke optimization because those companions will not level up and restore health.

I'm closing this issue due to inactivity. If further assistance is needed, please feel free to reopen or create a new.

I have changed board.lua around line 100
from:
info.followerGUID = follower:GetFollowerGUID()
local XPToLvlUp = 0
if info.isAutoTroop then
info.isLoseLvlUp = false
info.isWinLvlUp = false
to:
info.followerGUID = follower:GetFollowerGUID()
local XPToLvlUp = 0
if info.isAutoTroop or info.xp == 0 then
info.isLoseLvlUp = false
info.isWinLvlUp = false

and it seems to work4me ;)