What causes lines in the middle of a 3d print? Solve under extrusion problems mid print, halfway up!

So annoying when you come back to a print that was going well to find these naughty missing lines in it.
WHY DO THEY HAPPEN?!
Well, underextrusion and a partially blocked nozzle obviously. But there's more to it than that. Possibly.
No Eevees...were...harmed in the making of this video. Honest.

Please comment if you have anything to say!
Credits:
Music: Ouroboros Kevin MacLeod (incompetech.com)
Licensed under Creative Commons: By Attribution 3.0 License
http://creativecommons.org/licenses/b....

The Lift by Kevin MacLeod
Link: https://incompetech.filmmusic.io/song/5009-the-lift
License: https://filmmusic.io/standard-license

Voxel Revolution by Kevin MacLeod
Link: https://incompetech.filmmusic.io/song/7017-voxel-revolution
License: https://filmmusic.io/standard-license

Видео What causes lines in the middle of a 3d print? Solve under extrusion problems mid print, halfway up! канала Lost In Tech