Assignment allows submission in team mode: one student submit a file and the file "counts" for all members of the group that worked as a team.

Assignment correctly show the file link in the summary table for students and teachers. Teachers can click and get the submitted file without trouble. However, if the students try to access the submitted file they get an error message. Even the student that originally submitted the file.
So, if one member of a team uploads a file, the other members cannot see the content. The students cannot verify that the uploaded file is the right one before clicking confirmation (if activated).

The problem lies in teamsubmissions being stored in DB with userid=0. When assignsubmission_file_pluginfile() checks for permissions to see the submission associated file tries to test user with userid=0, that obviously do not exists.

assignsubmission_file_pluginfile() must get groupid fron submission data, in addition to userid, and must check specifically for teamsumission and the check if current $USER asking to get the file is a member of the group indicated in the submission data.