Both problems can be fixed by changing my protocol rule from honest chain's next block must include the nominations from any that occurred in the 6 second window to honest chain must include the nominations from all block solutions that occurred (with the same difficulty). Thus the difficulty has to be calculated counting all block solutions.
Thus chains can't diverge, except if they disagree about the difficulty. The objectivity about difficulty is a combination of using very long periods for the calculation so that difficulty is the same in calculations that differ only in small changes in the blocks included can't result in half or double the difficulty (since difficulty increments are a factor of 2 since they are the leading bits of the PoW with a 0 value),
Why don't disagreements in the set of all nominations cause the same forking problem that would occur with a fixed time window?
Also, isn't adjusting difficulty by factors of 2 is in danger of increasing the volatility of the currency? The cost of production will double or halve rather than smoothly increasing/decreasing as it does in bitcoin.