Printing Filatech PETG with HyperCube E3Dv6 Clone fails after 3 smooth layers
As this is material dependant, you are facing not a printer, but a settings issue: your slicer needs the right settigns to print PETG.

The first layers look good, but then we get signs of stringy printing. Stringy printing usually happens if the filament comes out of the nozzle too cold (I had tried to print PLA at 170 °C and it would look somewhat similar) or if it gets cooled or stretched too much (forced a print failure by speeding up a 60 mm/s print, somewhat similar around 250-300%; though the filament was not hot enough then too). This, in conjunction with the information, that you print PETG suggests the following things to fix:


Reduce or deactivate cooling. PETG often doesn't need cooling at all.
Reduce print speed. As 0scar said, 50 mm/s is a good upper limit on a well honed in machine. As your other layers with 30 mm/s were fine, you could possibly go down to 40 mm/s, if less cooling alone doesn't help.