Discounts not working

Discount for products is not working for 3.6 website. The discount for the category works just fine but for some reason it isn't working for the products. Has anyone else seen this issue and figured it out?

I discovered that if you accidentally have a 0 in the 'Maximum discounted quantity' the discount won't work for obvious reasons.  It mostly should be blank.

Using 3.9 and still seeing this issue. Discounts will not apply when "Assigned to Category" or "Assigned to Manufacturers". Discount will apply to cart (when using a discount code) but no changes are made to products or totals.

We have a number of manufacturers who do not allow discounts on their products so we are trying to apply discounts to all other manufacturers as a work-around.

Best