Chunks/holes spawning and multplying, black chunks, nether portal not functioning

So at first one hole spawned, my friend noticed it amd we were surprised, it wasnt a problem so we let it be, id say atleast like 7 weeks later i started mining underground and made a lot of progress for a project i was making, i saved and quit, when i logged back in there was a hugee chunk missing and it took my project with it, then i wemt to go see how much progress it took and it took 50% of what i was doing, i also realized it revesed time, because that 50% it took put blocks over it, there were four new holes one at my project, the second one took my friends house and farm, the third one was between my friends "house" and the once was first hole, the first hole is no longer there, my brothers horse and horse fell out of the world, my friends farm animals fell too. Second issue i started experiencing after the new chunks were the nether, i saw that if u go to the nether the chunks will reload and not ne there, i tried it and when i tried to return from the nether my portal spawned in my house, other then that my other portal no longer works as a return destination, but the third issue is black chunks, it doesnt bother me but i just wanted to include it in the problem.