EX7500 in existing Orbi (RBK50) environment

First, how is the signal strength there? How far away are you from the satellite? as FURRYe38  asks. What are your obstructions? Download something like WiFi Analyzer and check your signal strength in db. It could be just losing signal. 

If not, as a point of curiosity, I read nowhere that the EX7500 is rated for exterior use. If it is not totally exterior, why would you go with that product rather than an Orbi wall plug in like the RBW30 (it is obvious why someone may want to avoid the RBS50Y which is truly exterior: cost)?

The EX7500 is primarily designed for people who have an existing system that is not mesh. The term "mesh extender" is not used to indicate that the product is for extending mesh systems, but to turn conventional systems into a mesh type environment with a single SSID and that unit being a triband with dedicated backhaul. It also includes what Netgear calls "FastLane" technology, which allows you to dedicate some extender models bands to router connection but the EX7500 may work better not using this due to the dedicated 5GHz backhaul. How this is configured in your device may also be relevant to connection.using the EX7500 which is designed to turn a conventional wifi environment to a mesh environment, and not necessarily as an add on to an existing mesh system. For that additional add ons are offered. So if the signal strength is not the issue, settings for backhaul dedication on the EX7500 may be interfering.