Tvheadend

der all!

I read through the forums a lot, but I couldn't find a solution, so I'll have to ask:

• I run a headless tvheadend server HTS Tvheadend 4.3-2027~ge3f4f222e at the home network ip 192.168.8.2
• I configured all my channels with custom channel icons, and the tvheadend webpage at 192.168.8.2:9981 shows me the correct channel icons in the EPG tab, so that looks fine.
• configs are, amongst other things:
  > config > general > image-cache: NOT ENABLED
  > config > general > base: http sever settings ==> authentication type = "both plain and digest"
  > config > general > base: http sever settings ==> realm name = "tvheadend" (this is different from the username that the kodi-clients use, I guess this is ok)
• I run libreelec on Raspberry 4 with the tvheadend addon, and all the programs play just fine on my tv; I have a unpriviledged login, say MYUID:MYPWD for example

However, libreelec / kodi do not load the channel icons from tvheadend server: the ~/.kodi/temp/kodi.log file gives me errors:

2022-12-01 00:31:54.891 T:822 ERROR <general>: CCurlFile::FillBuffer - Failed: HTTP returned error 403
2022-12-01 00:31:54.891 T:822 ERROR <general>: CCurlFile::Open failed with code 403 for http://192.168.8.2:9981/imagecache/428:
2022-12-01 00:31:54.891 T:822 ERROR <general>: CFileCache::Open - <http://USERNAME:[email protected]:9981/imagecache/428> failed to open

So, somehow it seems to me that libreelec/kodi doesn't transfer the correct login to the tvheadend server.

and I guess the kodi clients use USERNAME=MYUID and PASSWORD=MYPWD and this is just not written into the login file.

but:
1: when I paste http://MYUID:[email protected]:9981/imagecache/428 into any browser on any pc on my intranet, the correct channel logo is shown.
2: I have the android TVHclient app installed on a tablet, and this app displays the correct icons, so the problem must be in the libreelec system

• I cleared all caches on the libreelec/kodi, even uninstalled an reinstalled the tvheadend addon
• I deleted ~/.kodi/userdata/Database/Textures13.db
  but this obviously didn't change the behaviour

What do I do wrong?