error: No appropriate assignment

[ViTe]

16:48:32:I1:WU1965:Retry #2 in 4 secs
16:48:36:I1:WU1965:Requesting WU assignment for user ViTe team 11897
16:48:36:I2:OUT292:> POST /api/assign HTTP/1.1
16:48:36:I2:OUT292:< HTTP/1.1 503 HTTP_SERVICE_UNAVAILABLE
16:48:36:E :OUT292:HTTP_SERVICE_UNAVAILABLE: {"error":"No appropriate assignment"}

Any ideas what's going on?
I see these messages for few days already. Sometimes machines cannot get an assignment for hour or even more.
It's definitely getting worse.
Linux Mint, Client 8.5.5, RTX 2080 and GTX 1080Ti