I have had a single player survival world since 1.16 and I have been updating it whenever a new official version of Minecraft comes out. I have never used this world on any snapshots and no cheats have been used. I have loaded parts of the nether in 1.16 up to 1.19. At around the (0,0) coordinates of my nether I broke through the ceiling to create ice paths for fast travel. I was creating a new ice path on the nether roof. I stopped at around (-2035, -20) because I ran out of ice, this was still when I was in 1.18. I stopped playing for around 10 days and in this time 1.19 released. I got back on after this and booted my world into the newest version like previous times. I got more ice and went back to keep making my ice path when at around (-2096 x, -670 z) I encountered 2 holes in the nether roof. Both of the holes were only 1 block wide. One was 7 blocks long, the other only 2. After seeing them, I pressed f3+G to show chunk borders and they were both on the borders of a chunk, 16 blocks apart on the z axis. I went through one of the holes to see what the nether looked like under it and there were signs of chunk blending nearby. in one place nearby a patch of glowstone on the ceiling was cut off with a hard line unnaturally and a nether ravine nearby changed on a hard plane which was on the same chunk border as the 7 block long hole. After this, I got the seed and went out to the same spot in the nether on a different world with that same seed in creative, but this time having all the chunks only be from 1.19. when I got there, there was no hole, meaning that in some way, updating from older versions to 1.19 caused chunk blending to freak out and break through the bedrock roof. The seed is 6086352378271497650. Below are screenshots of things previously described.