That would be a good option. Reset while the router is powered off, then when you power the router back on and it has connected, set the speaker up as a new device (taking into consideration the earlier information about ensuring the speaker and the smartphone is on the same network.)
It worked again after I unplugged the router dor 5 minutes, reset the speaker and then, add it to the app as a new device. If it's ok, I'll wait a couple of hours to check if this has solved the problem.
Thanks for your message, and sorry to hear that the issues are still ongoing. As noted within other threads, networking troubleshooting can oftentimes be troublesome, if not sometimes impossible, to perform accurately via platforms like a community forum due to a large number of third-party variables like independent router hardware, software, and available settings. Wherever possible, we encourage you to reach out to support directly in your region for one-to-one wireless networking support. Click HERE, select your location, and use the "Contact us" feature at the bottom of the page. We'll always be happy to help wherever we can on the Bose Community, but our resources are limited to directly assisting.
I can see that you've successfully accessed and updated your router's settings, which is great. We have some additional recommended settings for using SoundTouch speakers. See if you can apply these changes, and report back your outcome.
I believe the problem has been solved!
I bought a new router, and now the app works flawlessly on a 5G band.
Thank you so much for all your support.