@Daniel1234 

Like mentioned in the release note,  this FW has added some new features and fixed bug, it cannot be downgraded to former release once upgraded to this one. Back to your case, we can do some troubleshooting first to locate this issue and try to fix it. 

1. Are they still connected to the wifi but no internet access or they disconnect from wifi network totally in 3 meters away from the main router? 

2. Have you ever tried to change the wireless settings to improve its performance, including the wireless channel and channel width. And ensure that the transmit power is set to high.

Note: For 2.4GHz, using channel 1, 6 and 11, channel width as 20MHz; for 5GHz, using channel 36, 40 or 44 and channel width as 40MHz.

3. Try to adjust the position of the router or the antenna. 

4. You can hard reset it and reconfigure to give it a go as well. 

May it help.