I'm using the function UID ComputerID(Bool per_user) for an identifier for analytics. I also use it for the name of a save file.

We had a single case on an iPad when the ComputerID returned a different value without the user doing anything.
How safe would you say is the function on iOS and Android? Safe as in always returning the same value.

Hello,

The best way is if you would go to the source code of that function, and you can see what parameters it uses to build the ID.
I can't really say anything more about it, because it just depends on what values does the system return.

I have checked the code. An educated guess would help as well.

Could you try checking the output of
OSName();
OSUserName();
GetMac();
Maybe one of these are returning different outputs. because the generation of UID should be the same as long as the input is the same.