PS I guess this build is 32Bit only? Hope you will stay on 32Bit as there is no mem leak reconizeable at all
As far as I know there is a memory leak in 32-bit builds but much less recognizable and therefore not noticeable at all. That said developers with much more skills are looking into fixing the leak.
PPS In this thread here in the Kodi Forum a Kodi 18 build is mentioned where the inputstream is working again with Amazon Video, any chnace to get those changes into your build?
The mentioned Kodi version is for Android and uses WeTek's DRM capabilities in Android. In LE you can try using unofficial plugins: LibreELEC