The problem might be that I have over 1000 speakers.

I use the same blueprint for all my requester stations, including a speaker to alert me if amounts are low. It's not displaying them all.

There is no hard coded limit for icons in the mod. I could speculate that there is a limit in the UI, but I really don't know.

I am wondering if over 1000 icons could even fit on the screen.

There aren't that many alerts yelling at the same time (usually), but there are that many speakers total.

I have a couple of hundreds - with no problems. But there is a delay in showing the alerts in the UI; that is because of performance. So if a alert is triggered and a couple of seconds later it is stopped, then the Mod UI will show nothing.

I waited several minutes at least. The chest was totally empty. Alarm should have gone off long before.

Hi. I am really sorry, that this is not working for you. With the things you told me so far I can not make a the problem.
Are you seeing the in-build alert on the bottom-right of the the screen?

I've turned it off, and set up a base-wide network for alerts, so can't test it now. Sorry.