[Lokasenna]

Yeah, it's the combination of loop + that Ultraschall function. The latter opens the file each time and runs through it to find the section number if you give. It does close the file afterward, but it looks like Lua isn't cleaning up quickly enough after itself.

I don't have time to test this right now, but try:

local function list_keys_in_ini_section (section, fn)
  local sections = {}

  local LOOKING = 1
  local WORKING = 2
  local DONE = 3
  local status = LOOKING

  for line in io.lines(fn) do
    if status == LOOKING and line:match("%["..section.."%]") then
      status = WORKING
    else if status == WORKING then
      if line:match(".+=.+") then
        sections.insert(line)
      else
        status = DONE
    end
  end

  return sections
end

function get_preset_list()
  local found_presets = list_keys_in_ini_section("menubox_EXAMPLE", reaper_extstate_ini_path)
  if #found_presets > 0 then
    preset_list = found_presets
  end
  -- number_of_presets, _ = ultraschall.CountIniFileExternalState_key("menubox_EXAMPLE",  reaper_extstate_ini_path)
  --  if number_of_presets > 0 then
  --      for k in pairs (preset_list) do
  --            preset_list[k] = nil
  --       end 
  --      for i = 1, number_of_presets do
  --         local preset_name = ultraschall.EnumerateIniFileExternalState_key("menubox_EXAMPLE", i, reaper_extstate_ini_path)
  --         table.insert(preset_list, preset_name)
  --      end
  --      return preset_list
  --   end
end