We've encountered a previously discovered bug that was apparently fixed in a previous version, but now is appearing again for our 3.3.1+ install.

Original bug report here:
https://tracker.moodle.org/browse/MDL-54952

Step 1. Create a new Moodle assignment using the following settings

I selected the following settings while setting this up:

Availability
Allow submission- 23rd March 2018 0:00
Due date- 23 March 2018 13:15

Submission types
no buttons ticked (which then disables the other options)

Feedback types
only tick Feedback files
Submission Settings- kept as default

Group submission settings
Students submit in groups – Yes
Require Group to make submission- No
Require all group members submit- No default settings
Grouping for Student groups: Poster group

Group mode
Separate groups
Grouping - Poster group

Step 3. Add feedback files to the students work, and grade them.

Step 4. Batch set all submissions to "Released".

Step 5. Login as a student and confirm the grades are not visible anywhere. And also as a lecturer see that the grades are not in the gradebook.