RBR750 / RBS750 AP MODE NOT ACHIEVING STABLE WIRELESS BACKHAUL

As a general rule, the closer a satellite is to the router, the better the backhaul connection will be.

In practical terms, it makes no sense to locate WiFi access points very close together, because the total coverage area will be not much greater than the router itself.

What Netgear recommends is moving the satellites to locations that provide coverage to the part of the building where coverage is needed.

There are suggestions that "somewhere around 30ft" is a good place to start.  If the ring light is blue, indicating a Good signal, then they can be a bit farther apart.  If it is amber, that is too far.  Of course, satellites need electrical power, so if 30ft happens to be in the middle of a room, that is impractical.

If not totally impossible, 100ft is very unlikely to work.

The 750 product appears to have 'quirks' that I am unfamiliar with.  Also in general, once the router and satellites have established a good backhaul connection, changing the router to access point (AP) mode should not have any effect on the backhaul.

That appears to be the issue.  Not the actual distance.