Moving events across a DST barrier changes the size of an event from 1 day to 2.
DHTMLX Snippets isn’t saving, so heres my sample code (from 2020, when DST occurs on 3/8):
JS:
        scheduler.locale.labels.timeline_tab = "Timeline";
		scheduler.locale.labels.section_custom="Section";
		scheduler.locale.labels.timeline_scale_header = "Sections";
		scheduler.config.details_on_create=true;
		scheduler.config.details_on_dblclick=true;
		//===============
		//Configuration
		//===============
		var sections=[];
		for(var i = 1; i < 200; i++){
			sections.push({key:i, label:"section " + i})
		}
		var days = 7;
		scheduler.createTimelineView({
    name: "timeline",
    x_unit: "day",
    x_date: "%D %n/%j",
    section_autoheight: false, // allows more than one line in the "record" cells
    render: "tree",
    column_width: 180,
    dy: 160, // min. record column height
    dx: 300, // record column width
    x_step: 1,
          x_size: 5,
    round_position: true,
    y_unit: sections,
          y_property:	"section_id",
    scrollable: true,
		});
		var start = new Date(2020, 2, 6)
		scheduler.init('scheduler_here',start,"timeline");
scheduler.parse([
   {id:1, section_id: 1, start_date:"03/06/2020 00:00", end_date:"03/06/2020 23:59", text:"Move me to 3/8"},
],"json");