So here's my story:
Basically, the update that specifically said in the description that it would fix all issues related to iCloud...messed up my iCloud world.
My iCloud world was honestly fine before that update. It was working as it should. I didn't do anything to it but store a few rare items in chests in that world for safekeeping, because anything could happen to my phone and I was way to far into the game to not have a world that could be uploaded into a new phone.
After that update, everything went downhill.
It started to not recognize that I even HAD an iCloud world, which was terrifying. I even deleted the app—thereby deleting my main, non-iCloud world and all of the stuff in it that I didn't bother moving to the iCloud world before it became unplayable. After re-downloading it, it started to recognize that the iCloud world existed but crashed every time I tried to load it.
I went on my other device, which had the same iCloud account (and thereby had a synced iCloud world) to see if it could load it, but it didn't. They both have the same result: When the loading bar is at about 40%, the app crashes. I even got a brand new phone (not because of the issue but coincidentally after it started) and it also had the same issue.
@505Games-Mobile please acknowledge that there are still major iCloud bugs out there and try to fix them.
To other players (especially those who haven't updated for whatever reason), please be aware that your iCloud world (or character, although mine is working fine so far) may not be stable. If you are like me and have all of your precious items in a chest in an iCloud world, I will warn you that you may suddenly lose access to those items.
To those who have the same issue (especially if you have found a solution)--If you have any way of accessing an iCloud world/or character that has the same or similar situation to mine (AKA crashing before/right after loading), please, please, please reply or shoot a post my way...much appreciated in advance.
I have tried the following solutions (without success)
-downloading my iPhone content to my laptop, factory resetting, and redownloading all of the content (please note that if you try this, all of your non-iCloud worlds CANNOT be accessed...by iCloud save or by iTunes save)
-resetting every combination of settings
-shutting down and starting up my iPhone
-deleting and redownloading the game
-getting a new phone with shared account (same results as with old phone--my new phone is the same type as the old one, an iPhone 6)
-changing iCloud back up settings
-deleting the last back up and going from an old world
Thank you for reading this post all the way through (I know it's really long). Please reply if you have any input for my situation. I didn't have any "triggers"—there was no settings change or new world generation or anything that might have caused it (the crashing issue). It happened abruptly so I don't know if it's my phone, a Terraria thing, or a general bug.