In Sylius we are using WinzouStateMachine where as example sylius_order state machine has declared 14 callbacks on one state.
If this will be customized and number of callbacks comes up to 16 and higher - the priority of callbacks will become randomized.
Sylius state machine callbacks from now on will have priorities declared. Ending at -100 with step of 100.
Please note that those priorities are being executed in ascending order. You can find all the new priorities at
Sylius/Bundle/CoreBundle/Resources/config/app/state_machine.
Be aware that if those priorities were customized, this would lead to problems. You should check and adjust priorities on your application.
For changes according to the API v2, please visit API v2 upgrade file.