Ok so i'm able to replicate the issue on a fresh install with just maps and views and a couple posts.
Given that I was able to replicate, I went ahead and escalated your ticket to our 2nd tier supporters for further debugging.
The issue seems to only be limited to the Blocks editor on the backend and doesn't occur when you use the classic method with a view to add a map with a list of markers.
What you can do in the interim is to add your map markers using the classic method with views.
This means that you will go to Toolset-> Views and add a new and then add the map shortcode using the Fields and Views button and the Marker shortcode as well.