I did not have this problem with Mojave - it started with the beta of Catalina, and is still happening. Does anyone know a workaround?
I have a wired 1Gb/s connection and a WiFi connection to the same network. Wired so that I can actually get 1Gb/s throughput, and WiFi so that features like AirDrop will function properly.
Every few days, I get a popup saying that my computer already exists on the network, so it has been renamed, today to "MacBook (3)".
It's not a huge deal, but it is annoying. I rename it back, and it lasts a few days.