The minimum access level required to show up in the list of users who can receive a reminder.

that's almost surely a memory consumption issue.

I determined few days ago with xdebug that adm_config_report if consuming about 30Mb of memory to render, and about half of it is for composing the user's list in print_user_option_list() or, more precisely, in project_get_all_user_rows()

Additionally, the server logs does not seem to report anything about the problem.

Maybe there is some missing/misconfigured parameter in httpd.conf

Here are the possible solutions:

1. Have a configurable minimum threshold for who can receive a reminder. Typically reminders are sent to internal staff. In our case, we would set this to developer.

2. Avoid populating the list in an array then dumping it, generate the output row by row. The way I would approach this is to pass a callback to an API that iterates through all matching rows. The API would do the printing of one row at a time.

Forgot to mention a third corrective action:

3. Use an auto-complete edit box. In my opinion, this is also very useful when the user knows the user name of another user. So rather than scrolling through a potentially long list of users, just type the user name.

I've updated the issue summary / description to reflect the proposed solution.