Comment by ValdikSS

The majority of desktop Wi-Fi cards/chipsets have buggy drivers that break mDNS discovery in one way or another.

To the point that I'd say that Wi-Fi drivers are the most offender in printer discovery problems, which also rely on mDNS.

Another issue that many mDNS applications, including KDE Connect, don't account on multi-interface setups and send respond to mDNS request using incorrect network interface: https://bugs.kde.org/show_bug.cgi?id=507972 / https://bugs.kde.org/show_bug.cgi?id=507954