This is due to there not being listings because the hosting can’t handle all of the API calls this older version is making. That causes the hosting to timeout on the request and this serves up no listings.
V4 has much more performant API calls, better caching, better error handling, which also means it will work on more “less than optimal” hosting plans, but there’s not a solution for V3 other than upgrading the hosting a little to get more power behind the plugin.