Did you guys resolve your issue with your Mongoose? I have a Mongoose 90s for my daughter i bought new in 2019, barely has 20 hours I bet. Same thing happened to me. I was riding, I parked it, then it wouldn't start. I was able to get it to start once or tice but now it hard over dead. Turns over but no spark.
I narrowed it down to the CDI. I found specs online for it here
https://www.manualslib.com/manual/1386957/Kymco-Mongoose-90.html page 239.
It says it should be roughly 5 ohms from Black, black/yellow, and blue yellow to greeen. I measure open on all three.
My problem is finding the correct replacement. The sticker on it say "30400-PTA7-900". I can't find it anywhere. I have found ones that look like it but do not say they are for the mongoose 90s. It also has an 8 pin connector which is unlike most of what comes up in the search.
If you guys know a reliable parts replacement site that would help.