Orbi RBR50 + Satellite wifi dropouts, wired/wireless setup

Hi all! I have a RBK50 system (RBR50 router + RBS50 satellite) which is giving me lots of trouble with the wifi connection. Let me explain my setup please:

Internet comes from the ISP router in bridge mode (acting as a modem only) -> wired to Orbi RBR50 router

Orbi router is wired to: 

• D-Link DGS-104 Gigabit switch
• LG TV
• Philips Hue Bridge

That D-Link switch is wired to:

• Wall ethernet port, usually connected to a MacBook
• A 2nd Gigabit switch (TP-Link TL-SG1005D)

In its turn, the TP-Link switch is wired to a Sony TV, Playstation 4 and Apple TV.

On the other hand, the RBS-50 satellite is wirelessly linked to the RBR50, for expanding the wireless coverage (it's around 13 feet away from the RBR50, in clear sight).

Lastly, there are a variety of devices connected wirelessly to the Orbi network: smart lights, Nuki Smart Lock, LG fridge, LG washing machine, NetAtmo Energy and Weather, some iPhones and iPads, etc.

The point is that I’m suffering very frequent wifi dropouts. The connection seems to freeze for a while and then recovers itself. But sometimes, that “while” is 1 or 2 minutes long (and sometimes even more!). It’s really annoying and it prevents me to use critical devices like the Smart Lock with reliability.

I’ve discarded some possible error sources: the ISP company says that my connection and modem is ok, and I've also checked all the ethernet wiring with a cable tester, replacing some damaged cables, but the wifi problem persists.

I've tried some Orbi configurations that I've seen in the forum, without luck. Any clues? Thank you so much!