Some JIRA '@mentions' are not showing all users due JavaScript and REST APIs filters

Summary

The @mention feature of JIRA is failing to find some users (mostly ones with names starting with the initial letter of the domain) because the javascript responsible for this feature performs a filter over the results of a query via a REST call which is limited to 10 results. The REST call returns users which match the query string (username parameter in the rest call) based on if it exists in EITHER the username, display name, or email address. Because normally the domain matches many users email address, searching for users starting with the initial letter of the domain, will be filtered out.
e.g: mike@mydomain.com may be filtered out when searching for m if there are many more users with @mydomain.com email address and at least 10 users alphabetically before mike.

Environment

Affected version: 7.0.0-OD-08

Steps to Reproduce

1. Create 11 users with the same domain email address. eg: @example.com
2. Name the first 10 users with Letters before e
3. Name the 11th user 'example'
4. Try to mention the user in a comment.

Expected Results

If you use the complete username, or display name, the user should always appear.

Actual Results

Using the complete username or display name, doesn't show the user because the rest api is returning 10 previous users (but not displaying them as options)

Notes

When troubleshooting, take into consideration that you may need to refocus the comment box for the search to be done: JRA-59304

Workaround

Partial workaround
Try with a different user value (if you tried with username, try display name, or last name). The last name value works particularly well as it is quite unique.

Confirmed workaround
Typing the first few characters of a user's name and hitting the TAB button will autocomplete and allow for the user to be mentioned (until you refresh the page) e.g. John = Joh...TAB