OpenLayers adding modify interaction while preventing new vertices on GeoJSON features

Question

I'm having the case where I want to add a modify interaction over GeoJSON (loaded from URL) that is created previously, while changing the existing geometry without adding new vertices, but I get new vertices created where the original geometry not changed (images below, unfortunately gif is large), the first image shows the original geometry

the second image shows what happen after I grab some end and move it.

this is the code I'm using:

fetch("url").then(res=>res.json()).then(
            (data)=>{
                let vectorSource = new ol.source.Vector({
                    features:new ol.format.GeoJSON().readFeatures(data)
                })
                let vectorLayer =  new ol.layer.Vector({
                    source: vectorSource
                })
                
             
                let modification_interaction = new ol.interaction.Modify({
                    source: vectorSource,
                    insertVertexCondition: false
                })
             
                this.olmap.map.addInteraction(modification_interaction)
                this.olmap.map.addLayer(vectorLayer)
                }

OpenLayers version is v6.4.3,

Answer 1

for my specific case, it seems the fetch request is called multiple times which lead to geometries stack on top of each other, had to prevent that and now i can modify the features without problem