Nthng

The shaders you want are disabled on low settings, that's just the way things are in CSGO, the middle ground here is to have a desaturated, slightly transparent texture. I know, it doesn't look realistic, but players must be able to identify the glass on all settings, so as to not create any unfair advantage.

https://developer.valvesoftware.com/wiki/Refract
 Note:Will not work when applied to world brushes.  Note:When being used on a model, you must specify $model "1".  Note:Multiple layers of the Refract shader will not render when applied on the same entity.   For refract you must use "Refract" shader, not "LightmappedGeneric". And use it on brush entity or model, func_brush is the best.   For me 1st option is working with every graphics settings.   glass_d - texture    glass_n - normal map    Create yours with VTFEdit.

The problem with refract is that it distorts, so imo not a very good choice for two way windows in a competitive environment.

Did you built the mip-map in the VTF? Have you built the cubemap? In any case this is to be expected from a texture with a 0.04 alpha value, 0.04 is legit super translucent. Showing screens and telling us exactly what you want might help us resolve your issue. We still don't know if you want refraction or not?
The thing you see might simply be the reflection, not the texture. Reflections tends to disappear at an oblique angle.
Also I would avoid using the $alpha parameter altogether, unless there are several versions of this texture. You can tweak the alpha channel of your VTF to match the translucency.

Insertion has glass like this. Anyway, that is related to gameplay and not at all a technical issue

1st option
Make a func_brush with this material:
2nd option
Just use this material:
All values must be changed for your map lighting and setup.

Remove the refractamount line. My guess is that refract is an expensive shader, thus is only available in high video settings.
If you really want your glass to be refractive (I don't think that's the case since there is no normalmap) you can put it in a LightmappedGeneric_DX9 clause or something. I'm not sure how that's actually done in CS:GO. Something like
    "LightmappedGeneric_DX9"
    {
          "$refractamount" ".5"
    }
Should work. If it doesn't, try to find an expensive material that has a similar looking clause.

Have you tried increasing the $alpha value? 0.04 is 96% transparent.