@MoviePhone
Hard to pinpoint whether a change in Roku OS or a change in the router's firmware/update causes issues like these. These issues and workarounds/fixes have been around for awhile but affect different users at different times.
Since you don't have access to the router currently, you should be able to connect it to your hotspot though in order to get it working. Just make sure you have enabled the 2.4ghz on your hotspot (or enable "maximize compatibility) in the hotspot settings. Then just use a simple password and you should be able to get the Express to connect to it in order to test/use temporarily until you can verify network settings on the router.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, 4802, 4850, Premiere+ 3921, Express 4k+ 3941, Streambar 9102