Weird coupon problem

Here is a weird one and have tried to search for it.

I have a coupon code, let’s say THEBEST123. This is applied to the product to discount it on a value basis and not percentage.

1) When I am NOT logged in, I can place all items into my cart and proceed to the basket. If I do not have a coupon, I can go through fine without problems.

1a) If I have a coupon, I enter this coupon code into the coupon section, page refreshes, however, there are no errors, and there is no discount applied.

1b) If I continue after applying the coupon but it did not apply the discount, when I create an account and proceed. It shows the discount that has been applied.

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2) If I am previously logged in, add items to the cart, I can enter the coupon and it applied immediately.

Looks like that the coupon would only apply if someone is logged in, and/or once in the payment screen.

I initially thought this was a cache problem, so I cleared cache, disabled it for testing. Still the same problem.

Thought it was a PHP timeout as well, so I increased the time limit.

Disabled all plugins, still the same.
Changed to Default WP Theme, still the same.

My guess, it is something to do with Woocommerce.