Hi!
I've found that column menu doesn't work properly when both columns.selectable and columnMenu are enabled. Just run this code snippet and try to enable/disable columns in column menu.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
<title>Kendo UI Snippet</title>
<link rel="stylesheet" href="https://kendo.cdn.telerik.com/2020.2.617/styles/kendo.default-v2.min.css"/>
<script src="https://code.jquery.com/jquery-1.12.4.min.js"></script>
<script src="https://kendo.cdn.telerik.com/2020.2.617/js/kendo.all.min.js"></script>
</head>
<body>
<div id="grid"></div>
<script>
$("#grid").kendoGrid({
columnMenu: true,
columns: [
{ selectable: true },
{ field: "name" },
{ field: "age" },
{ field: "pet" }
],
dataSource: [
{ name: "Jane Doe", age: 25, pet: 'dog' },
{ name: "John Doe", age: 71, pet: 'cat' }
]
});
</script>
</body>
</html>