If you have a mod that edits Race records and it was created before the 1.6 patch, you need to update the Attack Data section in your Race records. If you don't you'll find that hitting anything with a melee weapon from horseback is extremely difficult, as rather than an attack hitting things on your flank, it will only hit things only at a very small angle in front of you.

What you need to do:

1. Open each edited Race record and go to Attack Data.

2. Click Update Events.

3. You will now see a number of new events appear in the list (with the letters MC in them), you need to edit these to these numbers:

attackPowerStart_MC_1HMLeft
Dmg Mult: 2.20
Attack Chance: 1.00
Stagger: 1.00
Recovery Time: 0.00
Stamina Mult: 1.00
Attack Spell: None
Attack Type: None
Attack Angle: -90.00
Strike Angle: 85.00
Knockdown: 0.00
Power Attack Box ticked

attackPowerStart_MC_1HMRight
Dmg Mult: 2.20
Attack Chance: 1.00
Stagger: 1.00
Recovery Time: 0.00
Stamina Mult: 1.00
Attack Spell: None
Attack Type: None
Attack Angle: 90.00
Strike Angle: 85.00
Knockdown: 0.00
Power Attack Box ticked

attackStart_MC
Dmg Mult: 1.00
Attack Chance: 1.00
Stagger: 0.00
Recovery Time: 0.00
Stamina Mult: 1.00
Attack Spell: None
Attack Type: None
Attack Angle: 0.00
Strike Angle: 35.00
Knockdown: 0.00
No ticked boxes

attackStart_MC_1HMLeft
Dmg Mult: 1.20
Attack Chance: 1.00
Stagger: 0.00
Recovery Time: 0.00
Stamina Mult: 1.00
Attack Spell: None
Attack Type: None
Attack Angle: -90.00
Strike Angle: 85.00
Knockdown: 0.00
No ticked boxes

attackStart_MC_1HMRight
Dmg Mult: 1.20
Attack Chance: 1.00
Stagger: 0.00
Recovery Time: 0.00
Stamina Mult: 1.00
Attack Spell: None
Attack Type: None
Attack Angle: 90.00
Strike Angle: 85.00
Knockdown: 0.00
No ticked boxes