The web service is unstable. Don’t reimage the microSD. Pull the cord and connect again to recover the access again and check if everything is working again.
I use the balenaEtcher for the images:
microSD 64GB for the RaspberryPI3 - With successful image and verify from the app
microSD 32GB for the RaspberryPI4 - With successful image and verify from the app
I have connection to the Raspberry PI3 via http://foldforcovid.local, but no results with my Raspberry PI4.
The router clients table displays the Raspberry PI3 (foldforcovid) but not the Raspberry PI4. I changed to Ethernet cable for the Raspberry PI4 with no results again.
Can you please download a dev image version? It is available on the same dashboard page for download, but there is a checkbox for it. Afterwards you can do a balena scan from your computer and see whether it is shown in the list with found balena devices on the network. https://www.balena.io/docs/learn/develop/local-mode/