Team goal number reset after surpassing 256

Seems like you are using an external app and game ignore it. 

It will be a memory limit - for things like seasonal stats the chances of a user eclipsing the 255 limit would be extremely low. While there are other solutions that could be used the most likely one in-game is that its an 8 bit field meaning it goes from 0-255.

Your 256th goal would reset it back to 0, then the 257th and 258th would take you to 2. 

At 16 bits it would then cover the range of 0 to around 65,000 which isn't necessary for 99.9% of the instances that occur in game and wouldn't be worth changing for the rare scenarios it does get exceeded.