It seems it had to do with the deferred shaders from another package which I'm using to deal with the foliage. There was no conflict with the shaders before, so it never occurred to me they might be the reason. Though I still can't wrap my head around how editing the script which disable Substance could cause the issue with shaders. The red error in the console still persists but seemingly cause no trouble no more - I'm able to enter the playmode and building the build seemingly works too. I'm loosing some additional features on the grass though, but that's another story. Thank you for pointing out that everything worked without errors on your end, it made me check additional possible causes of the problem.