That's good data about the AC relay contact surfaces. So maybe they can be ruled out as culprits.
Consider that the resistors are not in the circuit during charging, they only carry AC power for a very brief time during the initial pre-charge at OBC start up. There is a chain of abnormal events (culprit) leading to the resistor failure (symptom). Just replacing the resistors without correcting the root cause does not solve the problem. Unfortunately it is difficult to test an OBC to troubleshoot this circuit.
Maybe the 5V supply circuit has been compromised by a previous failure, or was the root cause of the initial 4.7R resistor failure?
Without knowing the culprit it is difficult to determine what might be a good solution, e.g. adding large capacitor to the 12V supply.
There are external factors to consider in addition to the internal OBC circuits