In case you havent had reports of this long standing bug here it is again.
When forming a group, you occasionally lose the group leader. This can happen on zoning or randomly. Ive had it happen between inviting one person and inviting the next.
Working solution is to disband and regroup and pray it doesnt happen again.
Attention Zenimax: Stamina builds don't hold up to magicka builds, and this is causing most of your class imbalance. It makes melee weapons and bows weaker than staves and class abilities. It makes medium and heavy armor less desirable than light armor. Fix this imbalance, and you'll address most of your balance issues.