RBK853- Devices often struggle to connect to network

Thanks for the response!

The modem unit is from my local Italian ISP- "TIM" called the TIM HUB but its an older model from 2016 (so maybe that could be an issue?). The connection we have is a DSL one with speed about 50 down/20 up. I think i should also mention that the modem doesn't have a bridge mode and I'm running RBR in router mode. But when i tried running Orbi in AP mode the issue persisted so I'm not sure if this setup is related to the issue. I switched back to router mode as i started having other problems related to wifi streaming when running in AP mode. 

The home is a fairly big old concrete building, which is why i had to get 4 satellites, but they are all hardwired to the RBR850. The closest two satellites are about 8-9 meters from each other (≈28 feet) but they got 2 thick concrete walls between them so they barely overlap in coverage. 

The channels are already at "1" for 2.4Ghz, and "40" for 5Ghz

20/40Mhz Coexistence is disabled, i dont think i have an option to specify 40Mhz only..

CTS is already at 2347

Preamble mode is in Auto (in case that matters) 

Let me know if you have any other questions)