Why are Android to iPhone data transfers failing after the iOS 18 update?

Hey there Apple community.

I work in a repair shop and one of the annoyances we usually get is when a customer decides to move to a IOS device since IOS update 18.

Usually we'd set up the transfer it would transfer everything even the Whatsapp chats. However after IOS update 18. Not a single customer that has moved from Android to Iphone has had a single successful transfer (I'm talking 32 customers sofar). We've had to resort to using Shareit to transfer anything over and then the customer loses their whatsapp chats because theres no other way to do it without paying for some license.

The problem? Every single time it gets stuck on the last few files of the whatsapp transfer. We've tried resetting, software updates, clearing all but 5 whatsapp chats. Now the funny thing is even when you deselect whatsapp chats, it then gets stuck on the last images. (I've let it run upto 5 hours and overnight at some attempts)

So what can we do to help our the transfer actually finish with all the content selected.

[Re-Titled by Moderator]