Seems there's an issue when adding a new Performance monitor to a Device Template that already has existing monitors.

When you add a new monitor and click OK, all the previously existing monitors are removed and only the new monitor is listed.

Please review the following screenshots:

1. Device Template with Monitors associated.

2. Adding a new Monitor -- Existing monitors show a Checkbox.

3. When expanding the Monitors page to 100,500 or 1000 items to display, the Checkbox next to each monitor is Cleared. [ISSUE]

4. If you select a new monitor now and click OK, only the new Monitor is added, all existing monitors are removed.

I am running version 12.3.119.