OK, I like this one better
It looks like a remote control application. I will say that maybe the oscillator quality is not fantastic on either its Design values or layout on the PCB.
Stand alone, depending on how you use the Stop Modes to save power, the application may seem to work fine. However, on the becnh when you try to program, Resets or clock trouble will show straight away.
Also, it is possible that the part is secured. The application will run perfectly, but you would need to unsecure it to get a proper dialogue.
Another one, is the XTAL at 8MHz a fundamental frequency or overtone ? if the latter, it would explain why it doesn't stay at 8MHz.
If you are using a scope probe on the oscillator circuitry to check the frequency, do make sure you are using a low capacitance probe (<1pF). If you use standard probes (10pF), its capacitance will interfere with the oscillator values and change everything.
The S08Rx family is quite robust. I have worked with it and the only trouble I had was with a oscillator misplaced: too far from the MCU and with power tracks running along the LED powering tracks.
Kind Regards,
Alban.