Factory reset after firmware upgrade

Yeah, it's unfortunate that Netgear hasn't updated their configuration system to deal with this.  Since a lot of consumer grade router firmware are derived from a common codebase, I would not be surprised if other vendors have the same problem.  Not all do.   I believe there is at least one that has bitten the bullet and fixed this problem.

Unfortunately, with Netgear you are stuck for now with doing the factory reset.   Worse, you can't rely on the backup file to restore from because it will be based on the previous version, so it may be incompatible.  There is a chance that you can get away without doing a reset if you don't use a feature that was subjected to the change.  A lot of people take this chance.  YMMV.