@Pherscho 

Hello, sorry that it is not allowed to downgrade to the previous version, please help confirm some details and we can try to fix it together.
1. What is the current network diagram? How many Deco M4 in your network? How are they connected?
2. How do you make it back to work after the LED turns red, do you need to restart the whole Deco system or it will recover automatically?
3. When the Deco M4 shows a red LED, with a computer connected to the main Deco M4 directly, can you access the internet? Try to simplify the network diagram, in other words, connect the main Deco to the modem only and then connect your computer to the main Deco to verify whether it works well.
4. Besides, you can try to relocate them and swap the locations of Deco units.
5. Additionally, you can leave the main 2.4GHz disabled and turn on the guest 2.4GHz, let those 2.4GHz clients connect to the guest network to give it a go.

Thanks.