Orbi RBR760 satellites stopped giving full speed.

[Poekie]

Hi everyone, 

Recently I moved, and I bought an Orbi system to give full coverage in our new home, and to connect my computer with ethernet. (Router is on first floor, computer is positioned on floor lower)
At first, everything worked like a charm. Getting full speed and coverage trough the satellites as i would expect. 
However, since 3 weeks the satellites are giving me some problems, and I' m not getting my full speed anymore as I was getting before. 

The setup is like this : I have a modem from my internet provider (Telenet in Belgium). The router model is : Docsis 3.1 E-router. 
I wired the Orbi RBR760 router to this one, and then placed the 2 satellites. 
I have a subscription with my provider for 1Gbps, and I was getting these speeds when I was wired to my satellite. I was getting around 950 Mbps. 

Now I' m only getting around 350Mbps, and I have changed nothing to the setup. 
When I connect my laptop to my modem wired, I get the 950-980 Mbps, and same when I connect it to the RBR760 router. 

I was able to solve this problem temporary by unplugging the satellite from power, and plugging it back in after +- 10 seconds. Than I would get my original 950 Mbps back for about 4-5 days, but this doesn't work anymore either now.. 

I already tried by swapping my 2 satellites, maybe there was 1 defective unit, but this didn't help either. 

The satellite that is connected with my computer has a 5Ghz connection with the router. 

What is going in here that I suddenly get less than half of the speed I was getting original, while I changed nothing? 

Edit : All connections where made with a CAT 6e cable

Thanks in advance for any help, 

[FURRYe38]

What is the size of your home? Sq Ft?
What is the distance between the router and 📡 satellite(s)? 30 feet or more is recommended in between RBR📡 and RBS🛰️ to begin with depending upon building materials when wirelessly connected.
https://kb.netgear.com/31029/Where-should-I-place-my-Orbi-satellite ‌‌🛰️

What channel configurations are currently set on the router? 

If 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...