[tor-relays] Exit relay: ERROR -- No Descriptor Available

[raspitor]

After running an exit relay for a few days I see the message: ERROR -- 
No Descriptor Available on the torstatus.rueckgr.at site, and the 
traffic of my exit node is almost zero, also seen in nyx. Rebooting the 
system restarts everything normal and it is listed on the ruckgraet 
site, but after a day or so the problem occurs again.
What might ne the cause of this?