Replying to myself: this is correct behavior according to Bosch CAN spec. The TEC is not incremented past 128 for ACK errors.

Hi,I encounter the same problem on a STM32H743. The tec value in ECR stop incrementing after 128, and bus-off state is never reached.This can be reproduced very easily by simply having only 1 device on the CAN bus. Sending a message should trigger BU...