Is this a current issue? I can't believe that you run that on a phone. I had problem like this, but it was a long time ago and it solved by itself. I don't know if it is true, but I listened that CSGO trade sites have some problems like this too, especially on phones. Last years I noticed that csgo trade bot is more engaging and I wasn't disappointed. The more, do you know that CSGO trade bot is with the most adrenaline pumping in the game. since I have been started to earn money selling skins, I am obsessed in it.
I have converted the maps to Blitz3d format and redid all the lighting using gile , I'm using a single 1024x1024 lightmap for each level.
I use the proton sdk which has a functional irrlicht port to load and render the levels on android.
The performance is pretty good, I get a constant 60fps in de_dust and fy_pool_day , and 55fps average in cs_assault, ofcourse you would know these maps if you have ever played cs
I will upload the apk if anyone wants that.