Getting "Couldn't import episode...Access to the path... is denied

4.0.9.2244:
Mono version (if Sonarr is not running on Windows): N/A
linux debian 12:
Hotio and LinuxServer image
Postgresql database

Debug logs:

Couldn’t import episode '/mypath/…/myfile.mkv: Access to the path ‘/mypath/…/myfile.mk’ is denied.

System.UnauthorizedAccessException: Access to the path '/mypath/myfile.mkv' is denied.
 ---> System.IO.IOException: Permission denied
   --- End of inner exception stack trace ---
   at System.IO.FileSystem.DeleteFile(String fullPath)
   at System.IO.File.Delete(String path)
   at NzbDrone.Mono.Disk.DiskProvider.TransferFilePatched(String source, String destination, Boolean overwrite, Boolean move) in ./Sonarr.Mono/Disk/DiskProvider.cs:line 422
   at NzbDrone.Mono.Disk.DiskProvider.MoveFileInternal(String source, String destination) in ./Sonarr.Mono/Disk/DiskProvider.cs:line 325
   at NzbDrone.Common.Disk.DiskProviderBase.MoveFile(String source, String destination, Boolean overwrite) in ./Sonarr.Common/Disk/DiskProviderBase.cs:line 263
   at NzbDrone.Common.Disk.DiskTransferService.TryMoveFileVerified(String sourcePath, String targetPath, Int64 originalSize) in ./Sonarr.Common/Disk/DiskTransferService.cs:line 495
   at NzbDrone.Common.Disk.DiskTransferService.TransferFile(String sourcePath, String targetPath, TransferMode mode, Boolean overwrite) in ./Sonarr.Common/Disk/DiskTransferService.cs:line 386
   at NzbDrone.Core.MediaFiles.EpisodeFileMovingService.TransferFile(EpisodeFile episodeFile, Series series, List`1 episodes, String destinationFilePath, TransferMode mode, LocalEpisode localEpisode) in ./Sonarr.Core/MediaFiles/EpisodeFileMovingService.cs:line 147
   at NzbDrone.Core.MediaFiles.EpisodeFileMovingService.MoveEpisodeFile(EpisodeFile episodeFile, LocalEpisode localEpisode) in ./Sonarr.Core/MediaFiles/EpisodeFileMovingService.cs:line 87
   at NzbDrone.Core.MediaFiles.UpgradeMediaFileService.UpgradeEpisodeFile(EpisodeFile episodeFile, LocalEpisode localEpisode, Boolean copyOnly) in ./Sonarr.Core/MediaFiles/UpgradeMediaFileService.cs:line 80
   at NzbDrone.Core.MediaFiles.EpisodeImport.ImportApprovedEpisodes.Import(List`1 decisions, Boolean newDownload, DownloadClientItem downloadClientItem, ImportMode importMode) in ./Sonarr.Core/MediaFiles/EpisodeImport/ImportApprovedEpisodes.cs:line 158

Description of issue:

I have a dockerized sonarr on linux debian that is not able to import downloaded file into the media share.
This has perfectly worked until recently.
The source (download) folder as well as the destination folder (media) are mounted shares (smb). Both are configured as full r/w access for owner/group/others (777).
Host access: Access to both source and destination from the host machine is available in read and write access.
Guest access: Access to the shell of the container proves read and write acces is ok to source and destination folder. Touch to the source and the destination folder is ok.
I tried image from hotio as well as linuxserver
Don’t understand where the issue lies.
Don’t know what else can be checked in order to find the root cause.

I really would appreciate any suggestions and help.

Thank you

Kptn