AngularJS: Select filter stops working after so many values

Job ID: 33516177

Budget: £10 – £20 GBP

I have a ui select filter on my application that does not show the values properly after a certain amount of values.

This: https://embed.plnkr.co/lWUBC7/

Previously, I was able to search values fine and when typing in the search box, it would send an API call in order to retrieve the values matching the entered information. However, once more values were added, it stopped working. I assume the code is okay, but the front end can't handle the performance. Need help, can share screen or send code, ideally the latter.
Related categories: JavaScript AngularJS