After searching on low-power-hardware I found a thread in this forum (https://discourse.fullandroidwatch.com/t/low-power-hardware-device-does-not-support-sending-files/47972) about connecting to C8 as a low power consumption bluetooth device. I manually tried to connect to it and managed to get a connection. After that I tried watchdroid again and I got a very unstable connection.
Then I tried to disable the backgroundcleaner for watchdroid, resulting in a more stable connection. But it still disconnects sometimes. My watch is around a month old.