Currently, those devices will quickly appear and disappear, giving user no way to reconnect. For example, https://bugs.kde.org/show_bug.cgi?id=458940

Temporary workaround: go to Settings > Advanced Settings > Erase saved devices cache

Potential solutions: allow user to pick wether to trust the new certificate, ignore the device, or maybe a new section for devices with changed certificate. Need to investigate how Android/Qt client is handling this.