Thanks Atom, but don’t waste too much time on it.
After further testing, I found out that the limit is the value “Maximum value the modulator can have should be set from the UI component” in the Modulator tab. It is not editable but grows automatically while you populate the list. I think it got stuck to 296 somehow while I copy/pasted the combo content.
Now I’m trying again on an empty panel with onli a uiCombo and it is working correctly up to 450, so maybe this was not a real problem.
The correct way would be to populate the list from the resources but that’s above my LUA skills.