Are you using different passwords for the 2.4ghz and 5ghz bands of your network? Unless you own one of the newer Roku Express 4k/4k+ devices (3940/3941 models), your Express will be connecting to the 2.4ghz band, while your Roku Streaming Sticks and RokuTV are dual band and can connect to either the 2,4ghz or 5ghz band.
Each wireless band is capable of having a different wireless password so that would be first thing to check.
In furtherance of the above, verify that your 2.4ghz band has not been disabled by your ISP (internet service provider). Some ISP have reportedly turned off 2.4ghz capability to their users, requiring a phone call to them to enable it again. If the case, make sure the 2.4ghz band is also configured to use Wireless Mode b/g/n (rather than just g/n or n only) since some ISP router firmware updates have affected some 2.4ghz devices negatively, requiring all three protocols (b/g/n) be used to work properly.
If you are able to connect your Express devices to a mobile hotspot (if available to you) on the 2.4ghz band, then points to a configuration issue with your network's 2.4ghz band.
Roku Community Streaming Expert Just another Roku user... I am not a Roku employee. Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102