From past long experience with FX3, the only case where we have seen a very high frequency of link errors is not recoverable. When FX3 gets into such a situation, any number of recovery attempts do not help and we keep cycling through recovery. The error threshold (64) was brought in as a work-around for such cases.
FX3 uses the LNK_ERROR_COUNT register to track the number of link errors logged by FX3. The register is cleared periodically (every 1 second). If we see that the count is reaching 64 errors (within 1 second), we power cycle the PHY. In many cases, this helps recovery. This reset feature is intentionally implemented for above reason.