What could be the reasons for this printed failure?  

RE: What could be the reasons for this printed failure?

It's called warping.
You can try this to prevent it: https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-how-do-i-print-this-printing-help/how-to-print-brim-ears/

Greetings,
Yveske

RE: What could be the reasons for this printed failure?

Thanks. Do things related to PLA warping also apply when we talk about  PETG warping? 

I seldom have warping issue. I think maybe once or twice out of 30 prints. However, when I printed this, I had the i3 MK3s inside an enclosure that has a big fan at the top to suck out the fume. Could the fan ruined the printing? Before this, I also had issues with all prints inside the enclosure. For example, during Z-level calibration, the filament did not stick to the rugged build plate, some filament balls like the one next to the warp. What do we call those filament balls? What are the causes?

RE: What could be the reasons for this printed failure?

First I won't pretend to know everything, I'm only into 3D printing for 10 months.

You can have warping with all kinds of 3D printed materials. I assume it has to do with parts cooling at a different rate.

As far as I know you can have blobs when changing nozzles and not reseating them correctly. This allows molten filament to escape via the threads. Another possibility is when you're printing or oozing filament mid air. Filament without underlaying support forms a little sausage hanging from the nozzle which is caught by the first edge the nozzle encounters or if you're unlucky it forms a mega blob around the nozzle.

Greetings,
Yveske