It's possible that there are multiple file names in single parameter, for example:
<sky-box texture="0006.png 0001.png 0004.png 0002.png 0003.png 0005.png" ... />
now it should work.
Also use is_opaque rather than has_alpha that gives better results.
The issues on android 4.4 + qualcomm should be already fixed in 8653d410f8a3a35175e87d413bc3229bbb9f8fae and d44802a4825f765645d63bca25ef697a83a47ce7
I also added few lightweight tracks and karts to the apk