Yes, this is quite certainly the problem. Make sure you have the current tvheadend42 addon installed. Kodi log will show that info, just use the logfile uploader in LE settings and post the link here.
BTW: very often (addon) update problems are caused by slow network initialization (kodi log will show that, too). Enable "Wait for network" in LE settings makes sure the network is up before kodi start and fixes these issues.
so long,
Hias
Thanks for your help but it seems i could solve my problem
.
Wait for network in LE settings was already aktive (10s). I have additionately activated maximal time to wait for network in KODI-settings and have set it to 20 s. Now tvheadend-server starts up without any problem and ... also without this change tvheadend-server starts up without problem now.
It appears to be a little bit curious for me because i have not seen any similar problems in the past using libreelec from the first releases until now (and openelec before).
I see 
- maybe the real reason for solving the problem is the update to tvheadend-plugin 9.1.900.119. There was only 9.1.900.118 available some minutes before.
Anyway - thank you for your quick service