They simply are not visible if they are saved with any earlier version.
Also, desynchs seem to happen when a player uses terrain editing tools or so (not directly and not always, but if editing enough, it seems to desynch; at least able to replicate this thrice)
I am afraid that I cannot reproduce the first problem: can you be more specific about which versions that it affects?
As to the second issue, which terrain editing tools seem to have this effect?
The general raising of land and the artificial slopes.
As for the first-- I had replaced the config folder with a new one from a fresh compile and this seems to have done it. Reverting, it can load again.
Does this desyc occur even on an empty map?