After a M4 (v3) firmware update to 1.6.1, my mesh is instable. The update was pushed in my management console of the Deco app. I have 3 M4s in my mesh and the slaves are loosing connection to the master, which means: no internet. Even if the slaves have connection, the speed is very bad (8MB instead of the expected >250MB). 

I rebooted the M4s after the upgrade (removed power supply for > 1 minute), no resolution.

I removed the slaves from the mesh and put them back in, but no resolution.

I tried to downgrade the firmware to 1.5.0 in the web portal, but apparently you cannot downgrade to a lower version. (why???)

What can I do? Before the update my mesh was working fine for over 2 years. Now I cannot work at home, since my internet connection is lost, slow, or can't be trusted.