hcan1 not working while hcan2 does work with same settings

I'm working with a custom STM32F105 board with two similar CAN circuits but CAN1 is not working.

I use STM32 HAL with this custom CAN lib which handles configuration and buffering.

It was working before with the same hardware but I can't get it woking anymore.

// create CAN instance
tSTM32_CAN &CANbus1 = *( new tSTM32_CAN(&hcan1, tSTM32_CAN::CAN250kbit) );
 
// enale CAN
CANbus1.InitCANFrameBuffers();
CANbus1.CANOpen();
CANbus1.SetCANFilter( true, 0, 0x00000000, 0x00000000 );
 
// Send message
void sendCANRequest() {
	if (CANRequestScheduler.IsTime()) {
		tSTM32_CAN::CAN_message_t message;
		message.id = BMS_Messages[BMS_Message_i];
		message.len = 0;
		message.flags.extended = true;
		CANbus1.CANSendFrame( &message );
	}
}

If I replace &hcan1 with &hcan2 and connect to CAN2 it works fine.

CANSendFrame in the end calls HAL_CAN_AddTxMessage which returns HAL_OK.

The 3 TX mailboxes fill up but the message just never gets sent out.

I also checked the filter function which should not matter for sending but it works fine.