...or there has been an FMC failure and software reset to the other FMC. Thus, there will be a period where the aircraft doesn’t have LNAV capability.
You made this statement previously and you were told then that your understanding is incorrect. With both FMCs operating normally, one of them is active and the other is inactive. The active FMC synchronises the inactive FMC any time there is a change to the flight plan or performance data. If the active FMC fails with the FMC selector in AUTO (ie the usual position), there will be an automatic failover to the previously inactive FMC, which already has all the data it needs to take over as the active FMC. There is no "software reset" and LNAV remains engaged.
Indeed, LNAV capability remains available even if both FMCs fail. In that case, the alternate navigation system uses the flight plan data stored in the internal memory of the CDUs; however, LNAV must be re-engaged.