Issue Summary

When using the Move function to change an issue's project we provide multiple UI warnings about the potential side effects of doing so. 

We do not state that the assignee field will not be updated during the Move, even if the issue's assignee doesn't have the Assignable project permission in the target project.

Steps to Reproduce

1. Create two projects and only give a user the Assignable User project permission in Project A. In Project B the user does not have this permission.
2. In Project A assign an issue to the user.
3. Go to the assigned issue and click the three dots [...] > Move
4. Move the issue to Project B
5. Observe that the the user remains the assignee of the issue which is now in Project B, despite not having the Assignable User project permission in Project B

Expected Results

The steps involved in using the Move function have UI warnings about the potential side effects of moving an issue to a different project e.g.
 

Your issues' destination project may have different settings than your source project. Even if they're named the same, issue types may use different workflows and fields. You may lose data when moving issues between projects.

A user might reasonably assume that all risks are enumerated in these warnings or the linked docs.

Actual Results

Neither the UI warnings nor linked docs mention that a moved issue can have an assignee in a project in which they don't have the Assignable user permission

Workaround

As with all Automation rules, be aware of your Automation service limits

The above would clear the Assignee value if it exists, regardless of that user's permissions, so it is not ideal. I think a more sophisticated version may be possible with a better conditional: https://support.atlassian.com/cloud-automation/docs/jira-automation-conditions/#Issue-fields-condition#User