Print cuts corners
How to fix?
RE: Print cuts corners
If those strands of filament are on your first layer then the problem is simple. Bed adhesion. They arent sticking to the sheet and so are pulled around.
Clean the bed thoroughly to remove all traces of greases and oils and then dont touch it with your fingers again. There are MANY threads on how best to clean the print surface so I'm not going over that again here.
Once your bed is properly clean the next step is to dial in the live Z perfectly. This will get a perfect squish. Once you have those 2 facctors dialled in then you wont have any more issues with adhesion. If you don't know how to dial in Z then read https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-assembly-and-first-prints-troubleshooting/life-adjust-z-my-way/
If the strands are not on the first layer then its the same basic reason, they aren't sticking, but this time to the filament below. This can be caused by not having the temperature hot enough for that filament or simply printing too fast so they don't adhere properly. Too much fan can also cause issues with over cooling but this relates to the temperature.
Find out the best temperature for the filament by printing a temperature tower and see what gives the best in terms of strength, overhangs and stringing.