Deco BE65 and Sonos App issue

Hello,
I have 2 x BE65 working in Access Point Mode connected wired as shown in the attached image.
Main deco 'Gelijkvloers' and satellite 'Boven'.
When my iPhone is connected to the main deco I experience no problems at all with the Sonos app
When I am connected to the satellite it usually happens that the Sonos app freezes and the internet connection on my iPhone drops
To be clear, all Sonos devices will remain connected and will continue playing. The problem only occurs on my iPhone.
I have also noticed that the problem does not occur when I work with a wireless backhaul.
How can I solve this problem? I still want to use the wired backhaul because it provides much better speeds.
Could it be a topological problem?
My system works perfectly otherwise, only when opening the Sonos app I may have problems. I previously had the Deco PX50 and never noticed that problem.
Thanks in advance for the help.
Gr.
Frederik
