Your custom UI module is applying global CSS overrides (like display: block, flex-direction: column, or width: 100%) that break the DynamicDataGrid’s internal layout, causing columns to stack vertically.
Fix:
Scope your custom styles (don’t apply them globally)
.dynamic-datagrid table
{ display: table; }
.dynamic-datagrid tr
{ display: table-row; }
.dynamic-datagrid td,
.dynamic-datagrid th
{ display: table-cell; }