Nextcloud version ( 21.0.1)
Operating system - nextcloud docker in unraid
PHP version _(eg, 7.4.15
The issue you are facing:
Is this the first time you’ve seen this error? (Y)
Steps to replicate it:
configured as ab smb/cifs external storage i can see all the files and downloads do start but end up failing every time
my next cloud docker is setup in unraid. Nextcloud is behind an nginx reverse proxy which all works very well.
anyone please 
Please use the search function of this forum FIRST nexyt time, before creating new thread covering a problem which has already been adressed in this thread.
i did and it did not help me. I sorted it out anyways this is how i got it to work for anyone else searching:
what i did was mount the share to the host (unraid in this case). Then i mapped that mount in the docker to the media folder. In nextcloud instead of SMB/CIFS (external storage) i used local