I have the following problem with my store(v3.60). I have 2 discounts that are applied to shipping price. Original shipping price is fixed at 4.5 euro. For orders with total price over 69 euros we use 100% free shipping discount and for orders with total price between 20 and 69 euros we use fixed -1.55 euros discount on shipping. I use the "Minimum order total" requirement.
Thus we have:
For orders with totals  from 0 to 20 - shipping is 4.5 euros
For orders with totals  from 20 to 69 - shipping is 2.95 euros
For orders with totals  from 69 - shipping is free
Also both discounts have requirement for shipping country - Greece.
Now this seems to work as expected in most of the cases, but every now and then we get an order in which a discount is applied when it shouldn't. For example an order for total price of 10.53 euros was placed which is nowhere near to the 20 euro mark for any discount but the store applied the 20-69 discount on it.
My main issue is that i cannot reproduce the problem both locally and on the live store. Also I've been looking in the code for the Minimum order total discount and couldn't find anything suspicious there.
So I will appreciate any hints that can help me investigate the issue and track down what is causing it.

Thank you.