problem with new generations on old maps

I am having a similar issue on MCPE (iOS). I loaded a couple of older worlds to see how the update would affect them before I went into my main world. The village in one was partly cut off, the hill behind it gone. We had explored that area before and I know there was a fortress there. Large chunks of the landscape are gone. I tested to see if they were just not loading by storing my inventory and jumping off the edge (very scientific, I know) and I did in fact die. 
I am new to this site but I will attach pics if possible. 

to correct this problem I have to delete some parts of my map in the nether and overworld making those parts update to the new version
 

for windows 10 there is this app to delete the chunks http://www.mcctoolchest.com/Download it took me about 6 hours to delete the chunks and keep my buildings in the overworld and nether and have it create the new structures.

sorry for the inconvenience these bugs were from a certain version a few years ago of that map i'm not sure which one was more in this version 1.16+ this problem does not occur and if it was due to some old version of the game that was affected. I really wanted to erase this pending but I don't know how I do it. thank you.

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We're tracking this issue in MCPE-58514, so this ticket is being resolved and linked as a duplicate.

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Its the 31 of Dec and I can’t get any presents from the 31 days of presents thing it just froze I got like half of them but the rest I can’t get it froze at the 24th present