I have a Linksys WRT3200ACM router that I recently upgraded to 21.02.1. That worked fine so far.Next I used the System/Software utility to upgrade packages. When I upgraded the hostapd-common package, all my wireless connections died. The radios show "Device is not active", the connections show "Wireless is not associated".
I had to reinstall the 21.02.1 firmware and stay with the original packages.
I strongly disagree. Especially on stable branches, package upgrades are supposed to work fine. If they don't, it is a bug that needs to be corrected. In this case the various hostapd backports were improperly done (e.g. no strong dependency version constraints, no check for availability of new features).
@eehmke: you need to upgrade both hostapd-common and the installed wpad flavor simultaneously. The updated scripts in hostapd-common rely on new features in the compiled wpad part which are not available with the older version.