Magento 2 – Multiple Cart Rules Not Working Simultaneously

I solved it myself!

Strangely, I had to put the current currency sign before amount. We are using INR (Rs.). So I needed to use "Rs. 2000" instead of "2000". So my condition is changed from (emphasis the difference)

• If ALL of these conditions are TRUE :
  • Subtotal equals or greater than 2000

to

• If ALL of these conditions are TRUE :
  • Subtotal equals or greater than Rs. 2000

After that change, I could apply the coupon successfully even with one step checkout:

The rule is working correctly as per the configuration.

Conditions tab:
If ALL of these conditions are TRUE :
If an item is FOUND in the cart with ALL of these conditions true:
Manufacturer is Adidas

This rule says if there is any item in the cart with the manufacturer as Adidas, then apply 10% discount to the whole cart and not just to the specific product.

If you want to apply the discount to the specific items, then you have to add the condition under 'Apply the rule only to cart items matching the following conditions'.