He encontrado esto precisamente en los comentarios d eun video de youtube, no sé si te ayudará:
Hi guy
if you want to fix wifi problem.
just use SD card class 4, because this tablet has some problems if you're using SD card class 10.
fix:
1/ unmount SD card
2/ Restart cube U30gt ( power off > power on )
3/ connect the wifi again
good luck