Thank you for your excellent simulator.
Do you have your own implementation to String::itoa function?
I think you have problem in there. when you use it to translate 123 to "123", it return "122" for example.
For more detailed example you can see my post here:
actually I tried to use the function String(123) to translate it' and i got the wrong value, so i checked in the GItHub of Arduino for the implementation they use itoa function for that. their implementation looks good, but when i run that function in the Tinkercad simulator it return wrong answer. so i guess this is the point.