I think in HAL CAN driver have error in function HAL_CAN_Transmit_IT
I put part of driver here https://pastebin.com/PhHcMC94
on line 13 we see
next on line 29 we see
and next execute only if statement true
If system haven't free mailbox hcan instense not unlocked. And i cant execute any funtion because his instanse locked.
I'm not sure that I'm right. If I'm not right, explain why it's written like that.