RBR750 and 2 RBS750, nightmares, almost non-usable

Your ISP Modem already has a built in router and wifi. This would be a double NAT (two router) condition which isn't recommended. https://kb.netgear.com/30186/What-is-Double-NAT
https://kb.netgear.com/30187/How-to-fix-issues-with-Double-NAT
Couple of options,
1. Configure the modem for transparent bridge or modem only mode. Then use the Orbi router in router mode. You'll need to contact the ISP for help and information in regards to the modem being bridged correctly.
2. If you can't bridge the modem, disable ALL wifi radios on the modem, configure the modems DMZ/ExposedHost or IP Pass-Through for the IP address the Orbi router gets from the modem. Then you can use the Orbi router in Router mode.
3. Or disable all wifi radios on the modem and connect the Orbi router to the modem, configure AP mode on the Orbi router. https://kb.netgear.com/31218/How-do-I-configure-my-Orbi-router-to-act-as-an-access-point and https://www.youtube.com/watch?v=H7LOcJ8GdDo&app=desktop
Try option #2 first...

Try setting manual channel 1, 6 or 11 on 2.4Ghz and 40 to 48 channel on 5Ghz.

Turn OFF the RBS and just test with the RBR alone for now. 

So the RBS are ethernet connected to the RBR? If so, how are they connected, is there a LAN switch or patch panel in between the RBR and RBS? Brand and model of switch if one is in use please.

Thanks for finding the reference.

You might consider the nuclear option of doing a Factory Reset.

https://kb.netgear.com/31486/How-do-I-reset-my-Orbi-system-to-factory-default-settings 

Use exactly the same WiFi credentials so that WiFi devices will not have to be configured again in order to connect.

It does not appear that Netgear supports Hebrew on this model (on any model?)  What language is used for entries? (SSID, passwords, etc.)

As you are aware, a Double NAT can make specific applications difficult to set up, but should have nothing to do with devices connecting to the Orbi LAN and receiving IP assignments.  When my Orbi is power cycled, everything is back on line within minutes. Never "hours" or "days".