Stopped playing/testing, got spammed with this ^
Never saw it before. Thought I'd post it.
What SDK and Unity version are you using here ? When exactly are you seeing this error ?
I'm getting this too... Unity 2017.1.1p4, SDK version 18.104.22.168. It happens when the code is retrieving API key and appears even in the sample project that comes with GameSparks. It doesn't seem to do any harm but my colleagues are complaining about the assert!
Unity 5.6.4 with GS 22.214.171.124