Asus C302 used to connect but now it’s not. It can’t find its Introducer (on Fedora 28), nor can the introducer find the Android on Chromebook. Other device in the family are fine…just not this Android on Chromeboook.
There are plenty of other threads which talk how to debug this. Try using the search first, and if what you find does not help, give us a shout.
You could try to run the native syncthing using the developer mode and/ or crouton because Android Apps are extra isolated which could cause problems.