There appears to be something strange that's going on with umdns with the OpenWrt 19.07.01 service release. While umdns appears to be running fine, it no longer advertises the router. I have been able to reproduce this problem on a Buffalo WZR-HP-AG300h and Linksys EA8500, as well as TP-Link TL-WR703n, and MR-3020. 19.07.0 works fine.
By contrast, avahi appears to work fine (except for the much larger footprint).