Duplicate features appearing in Field Map and Explorer

[PeterTQFES]

I have a hosted point service on our Enterprise Portal (High Availability) that is being updated every 2-3 minutes with a truncate insert.

In both Field Maps and Explorer I'm getting duplicate points and some duplicates have no attributes.

I have a timed refresh on the Map.

In the example below I've kept the app open for a while so I've got 5 duplicates appearing.

I also get this on another hosted service with a similar update process.

I DO NOT get this behaviour in our web app builder using the same map.

Any ideas what could be causing this?