I've also been experiencing this issue on a new world created since the 1.14.30 update. (Playing on Xbox one) This doesn't seem to occur on older worlds where I didn't have any issues. Sometimes the game was able to finish the "building terrain" screen, but the unrendered sections would not be the same across various attempts. This happened several times, but as stated above, I can no longer get past the "building terrain" screen when returning from the nether. However, I built a portal in a new chunk and it worked as expected. For whatever reason, the location of the portal seems to be at the root of the issue because I've moved the portal around the same area and have achieved the same buggy result.
Cole Draper
I've also been experiencing this issue on a new world created since the 1.14.30 update. (Playing on Xbox one) This doesn't seem to occur on older worlds where I didn't have any issues. Sometimes the game was able to finish the "building terrain" screen, but the unrendered sections would not be the same across various attempts. This happened several times, but as stated above, I can no longer get past the "building terrain" screen when returning from the nether. However, I built a portal in a new chunk and it worked as expected. For whatever reason, the location of the portal seems to be at the root of the issue because I've moved the portal around the same area and have achieved the same buggy result.