Add table-header-group display class

app/assets/stylesheets/bootstrap_migration.scss

@@ -52,6 +52,16 @@ table {
   pointer-events: none;
 }
 
+
+@each $breakpoint in map-keys($grid-breakpoints) {
+  @include media-breakpoint-up($breakpoint) {
+    $infix: breakpoint-infix($breakpoint, $grid-breakpoints);
+
+    .d#{$infix}-table-header-group  { display: table-header-group !important; }
+  }
+}
+
+
 // Polyfill deprecated selectors
 
 .hidden {

app/views/admin/abuse_reports/index.html.haml

@@ -5,7 +5,7 @@
   - if @abuse_reports.present?
     .table-holder
       %table.table.responsive-table
-        %thead.d-none.d-sm-none.d-md-block
+        %thead.d-none.d-sm-none.d-md-table-header-group
           %tr
             %th User
             %th Reported by