CAN-BUS line goes bus off state at high temperature(70C°)
Internal oscillators have larger tolerance and temperature drift than what is required for stable CAN communications.
For example, the F072 HSI8 has 2% tolerance over temperature range from 0 C to 70 C.
Depending on which CAN specs are being used, they either allow up to 0.5% or 1.5%.
In practice, at least a ceramic resonator should be used for CAN communications, preferably a crystal.