I made a survival world on my computer which I called "1.8 UHC" and I had the following settings:
Render Distance: 10 chunks
Graphics: Fast
I then noticed when I spawned that there was a black bar around the edge of the world, as seen in the first screenshot.
I tried to record this glitches that happened later on when i relogged but it wouldnt work so I just spammed f2 which gave me all of these screen shots.
I relogged again after my whole computer froze for about 2 minutes, shut down MC while it was 'Not responding' and then checked the screen shots.
I have no idea what went wrong but this affected my computer and caused it to work overtime . Also, my fps was weird
it jumped from 40-50 fps when i joined for the second time, to 1-6 fps, the I clicked escape and it had 1 massive jump to 968 fps, to which it retured to 6 fps. I then turned it off. Thanks to whoever replies to this and I hope you find a way to fix it. My world has now loaded fine and I am continuing to play it