There is this know issue with vray denoiser not working well with glass materials. Anytime I see the Denoiser Pass everything behind the glass looks terrible, smugged and Blured. This has been happening since denoiser was introduced and I’m wondering if its been solved in Vray 5. 
Can you let us know about what exactly are you referring to? There is a current issue on GPU mode concerning the Denoiser when a material’s All channels option is selected under Affect Channels - it produces different results in the Render Elements and has been thoroughly discussed in this forum thread. Our devs are working on it and I’ll let you know when there is a solution on the matter.
If that’s not the case, please share some example screenshots/recordings and maybe even forward a project we can test so we can investigate further. Thanks!
All channels in Affect Channels is working, but causes another problem when using section cuts – cutted geometry renders black in reflections. And everything is ok when Color Only in Affect Channels is selected, but the reflection is too blurry again.