Tvheadend

Hi everyone.

I have a TBS 6618 DVB-C tuner card in my htpc and I am using tvheadend with Kodi.
When the htpc has just been started everything works fine. I can watch tv, timeshift, record you name it.
After a period of time, sometimes minutes, sometimes hours tvheadend stops working. When I then try to watch tv the logfile says:

Okt 18 20:14:24 bigbrain tvheadend[24841]: subscription: 01D7: "127.0.0.1 [ Kodi Media Center ]" subscribing on channel "Das Erste HD", weight: 150, adapter: "TBS 6618", network: "TeleColumbus", mux: "402MHz", provider: "ARD", service: "Das Erste HD", profile="htsp", hostname="127.0.0.1", client="Kodi Media Center" 
Okt 18 20:14:30 bigbrain tvheadend[24841]: subscription: 01D7: service instance is bad, reason: No input detected
Okt 18 20:14:34 bigbrain tvheadend[24841]: subscription: 01D7: No input source available for subscription "127.0.0.1 [ Kodi Media Center ]" to channel "Das Erste HD" 
Okt 18 20:14:35 bigbrain tvheadend[24841]: subscription: 01D7: "127.0.0.1 [ Kodi Media Center ]" unsubscribing from "Das Erste HD", hostname="127.0.0.1", client="Kodi Media Center" 

And kodi of course gets no signal. After restarting tvheadend it works fine again, for a while.

Using tvheadend 4.0.9 on Arch linux (official package, not updated for a while).

Any hints how I can find the problem?