The wax additive only has a function while the resin is curing. It prevents the styrene to vapourise too much, wich would cause the resin not to cure properly at the surface. Which is exactly what happens (and what you want) with gelcoat, because the laminating resin then provides fresh styrene for the gelcoat wich results in a chemical bond between gelcoat and resin.

So your problem has nothing to do with thinning out the wax. It could either be undercured  gelcoat because of a too thin layer, wich causes the same vaporization  issues, or because of bad mixing, or because of not enough mekp.
Finally the gelcoat can be not suited for long exposure to the mould cleaner.

Greetings,

I recently did some repairs on my mould and after some sanding down, applied a layer of gelcoat with the wax additive included. Today, I decided to clean the mould with the Easy Lease mould cleaner in preparation for the release agent before doing some resin infusion.
However, I noticed the gelcoat getting tacky again with every swipe of the cloth and stopped. So my question, has anyone else experienced this?
Is the mould cleaner acting like a thinner and eroding the wax additive?