Home WiFi Issue - due to AirPort Express?

In theory, the AirPort Express might be able to handle 50 connections, but "specifications" like this are pretty much meaningless. For example, Apple does not tell you that the network would really start to slow down significantly at about 10 devices and probably become unusable at 20-25.

Frankly, your current requirements are beyond the capabilities of the AirPort Express, which was designed almost 10 years ago, long before the explosive growth of wireless lighting, home security and streaming services.

Time for a new router or mesh system if you need extended WiFi coverage throughout your home.

It’s old and slow, and old enough to be failing, and a crowded Wi-Fi is flaky, and Wi-Fi interference from other networks is subtle.

I’ve had Apple Wi-Fi networks just drop out from time to time. Ended up replacing those Apple devices.

It’s also possible that your ISP link is old and slow and dropping out, or under-rated for your needs, though.

Or that you’ve got a really busy Wi-Fi client. Video streaming is more demanding than audio streaming, etc.

The number of clients is less of an issue than the aggregate of the network activity.

To start... Use the “hidden” Wi-Fi performance display on your Mac and have a look at the data; option-click on the Wi-Fi menu item. Post the values for the Channel, Country, RSSI, noise, TX Rate, PHY Mode, and (if any) the total number of other Wi-Fi networks shown in the list below your own Wi-Fi you’re connected to.

Better: Acquire Wi-Fi Explorer or another tool for your Mac, and scan what’s available.

Your signal strength is reasonably strong, noise normal, speed is good, you’re getting two-thirds of the theoretical speed, but that many strong local Wi-Fi networks nearby is likely going to incur interference as folks get tossed around by channel re-selection.

The Wi-Fi Explorer app or similar can show you the other Wi-Fi users’ channels. (But again, somebody reboots a Wi-Fi router, and that then sets off a cascade of channel reassignments.)

The other limit here is your ISP and your network bandwidth.

Local preference for Wi-Fi replacements is Ubiquiti access points, but that’s a little more complex to set up, and you’l need to provide DHCP, firewall, and related services. Lower-powered WiFi with 802.11ac with MIMO is probably your path of choice.