When notifications was tested earlier in the development cycle, a user assigned to an issue would receive DM for may events where an issue was updated. This was separate from subscriptions functionality. DM were received from the Jira bot for things such as, Comment added, Issue type changed, Issues status updated.
This is no longer occurring. When I 1st saw this behavior, Michael investigated for me and determined this was not a bug. Now this behavior no longer occurs (on Cloud or Server)
To be clear: Users still receive a DM when they are assigned to an issue (as expected) or when an issue is created with the user as the assignee. This behavior is working normally. But future updates do not generate a DM (but should).
Install a Jira instance and setup a subscription webhook
Map the test user to a Jira user
Login to Jira as a 2nd User not the test user
Ensure notifications are working by @mention the test user
Assign test user to an issue
Perform several updated to the issue such as add a comment that does not contain a mention.
Observed No DMs are received on step 6. (step 5. generates a DM as expected)