I am having a problem with my docker installation for 8.2.0.  I cannot upload files, either to my avatar or to my work packages.  I receive the following errors: 

When trying to upload a new avatar:  "Error saving the image."    When uploading attachments to a work package:  "An internal error has occurred. Http failure response for https://<website>/api/v3/work_packages/17/attachments: 500 OK"

Looking at the "information" tab as the admin I see that the "Attachments directory writable" is a bug/alien so clearly there is an issue.   The openproject/static/files directory is owned by a user not in my host machine's /etc/passwd. When I go into the docker container I see that the owner is the user and the group 'app'.  The permissions are 750.  When I change the permissions of the files directory to 777 it does not fix the problems.

I verified that the container environment variable ATTACHMENTS_STORAGE_PATH points to the correct directory of /var/db/openproject/files.

Here is the error message I see in the openproject/logs/web-stdout.log (I removed my IP address):

App 441 output: Started PUT "/my/avatar" for [MyIPAddr] at 2019-01-29 04:18:31 +0000 
App 441 output: Processing by Avatars::MyAvatarController#update as JSON 
App 441 output:   Parameters: {"metadata"=>"{\"fileName\":\"HouseFace.jpg\"}", "file"=>#<ActionDispatch::Http::UploadedFile:0x00007f6a3eaf3bb0 @tempfile=#<Tempfile:/tmp/RackMultipart20190129-441-6ndlsd.jpg>, @original_filename="HouseFace.jpg", @content_type="image/jpeg", @headers="Content-Disposition: form-data; name=\"file\"; filename=\"HouseFace.jpg\"\r\nContent-Type: image/jpeg\r\n">} 
App 441 output: Failed to update avatar of Niels Lindenthal: Permission denied @ dir_s_mkdir - /var/db/openproject/files 

Any help greatly appreciated!

-Rob