<!--- Please read this! Before opening a new issue, make sure to search for keywords in the issues filtered by the "regression" or "type::bug" label: - https://gitlab.com/gitlab-org/gitlab/issues?label_name%5B%5D=regression - https://gitlab.com/gitlab-org/gitlab/issues?label_name%5B%5D=type::bug and verify the issue you're about to submit isn't a duplicate. ---> ### Summary <!-- Summarize the bug encountered concisely. --> When I update the milestone of issues using batch edit, the assignment of the modified issues is reset to empty. ### Steps to reproduce <!-- Describe how one can reproduce the issue - this is very important. Please use an ordered list. --> 1. I display the list of issues of a Milestone (https://gitlab.com/groups/henixdevelopment/open-source/opentestfactory/-/issues/?sort=updated_desc&state=opened&milestone_title=Sprint%2077&first_page_size=100). 2. I click on `Select issue`, select the first one. In the right panel, I select another Milestone.  3. I click on `Update all`. 4. Now, I display the issue I have updated: the assignees have been reset.  ### Example Project <!-- If possible, please create an example project here on GitLab.com that exhibits the problematic behavior, and link to it here in the bug report. If you are using an older version of GitLab, this will also determine whether the bug is fixed in a more recent version. --> The problem is present on https://gitlab.com/henixdevelopment/open-source/opentestfactory/. The problem occurred last Friday 5PM CET but I spotted the problem only this morning. It occurred on the previous group and on another private one. The problem is not present at projet level (I have done the same things on two projects where the milestone are defined at the projet level, the assignees were not lost). The problem was not present on Friday 2023-01-20. ### What is the current *bug* behavior? <!-- Describe what actually happens. --> Changing the milestone in batch edit removes the assignments. ### What is the expected *correct* behavior? <!-- Describe what you should see instead. --> Changing the milestone in batch edit does not impact the assignments. ### Relevant logs and/or screenshots <!-- Paste any relevant logs - please use code blocks (```) to format console output, logs, and code as it's tough to read otherwise. --> I included the screenshots in the scenario above. ### Output of checks <!-- If you are reporting a bug on GitLab.com, uncomment below --> <!-- This bug happens on GitLab.com --> <!-- /label ~"reproduced on GitLab.com" --> #### Results of GitLab environment info <!-- Input any relevant GitLab environment information if needed. --> <details> <summary>Expand for output related to GitLab environment info</summary> <pre> (For installations with omnibus-gitlab package run and paste the output of: `sudo gitlab-rake gitlab:env:info`) (For installations from source run and paste the output of: `sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`) </pre> </details> #### Results of GitLab application Check <!-- Input any relevant GitLab application check information if needed. --> <details> <summary>Expand for output related to the GitLab application check</summary> <pre> (For installations with omnibus-gitlab package run and paste the output of: `sudo gitlab-rake gitlab:check SANITIZE=true`) (For installations from source run and paste the output of: `sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true`) (we will only investigate if the tests are passing) </pre> </details> ### Possible fixes <!-- If you can, link to the line of code that might be responsible for the problem. -->