My 2nd generation AIRPORT EXPRESS keeps disconnecting from WIFI. It has the latest update. I use it for it's Airplay 2, for streaming music.

Easier on a Mac.

Connect an Ethernet cable from one of the Ethernet ports on the main router to the WAN "O" port on the AirPort Express

Power up the Express and let it run for a minute

Hold in the reset button on the Express for 7-8 seconds and release

Allow a full minute for the Express to restart to a slow blinking amber light status

Open AirPort Utility on the Mac (Finder > Applications > Utilities > AirPort Utility)

Click on the Other WiFi Devices button

Click on AirPort Express xxxxxx

When you click on the AirPort Express, that will start up the AirPort Utility setup "wizard" automatically. The wizard will take a few seconds to analyze the network and display a window with the correct setup for the Express. It will look like the example below except your version of the AirPort Express will be displayed.

Network Name......Type in the exact same name of the WiFi network that your router is using

Base Station Name......Type in a device that you want to call the AirPort Express

Password.......Type in the exact same wireless network password that your router is using

Verify.....Type in the same password again to confirm

Click Next

The setup wizard will automatically configure the Express with the correct settings. The Express will be set up to "extend" your wireless network and provide additional wireless coverage.

When you see the message of Setup Complete, click Done....and you are done.

Important......the Ethernet connection between the Express and router must be maintained at all times. You cannot disconnect the Ethernet cable.

Your chances of reliable connections will improve significantly if you forget about WiFi and connect the Express to your router using a permanent wired Ethernet cable connection.

If you cannot run the Ethernet cable, take at a look at a pair of Ethernet over powerline adapters to send the signal over the wired AC powerlines in your home. The theory with devices is that you already have the wiring in place, you just need the adapters.

Sorry, but the 2nd Gen Express was designed in 2011, so you are looking at 9 year old technology in the product, likely one of the reasons why it won't work all that reliably with a newer router.

I would expect two Apple products like an iPhone and Express to work OK since they were designed to work together. Not the case with an Express and 3rd party router.

Trying to configure the Express as a new network won't work unless you plan to leave it permanently connected to your router using the wired connection.

Can't think of anything else to try at this point. I have problems with a 2nd Gen Express trying to connect over WiFi to an Apple router. That's why I wire the Express back to the main router. Flawless results for months now with the wired connection.

What device......a Mac or iPhone.....will you be using to reconfigure the AirPort Express?

Fingers crossed, but you have improved your chances of good performance significantly.