This is actually general issue when use mix HTML+PHP and we need to insert code between, for this use case, I found at ForRepeatedCountToOwnVariableRector, which change to:

$itemsCount = count($items);<?php
+        for ($i = 5; $i <= $itemsCount; $i++) {
             echo $items[$i];
         }

when previous node is HTML, the code become invalid, The tweak is by re-print the previous/next node when previous/next Node is HTML.

see https://getrector.org/demo/5b00ff10-b7af-4465-bb5d-3e4727e4c948

This is not perfect as it cause unnecessary empty <?php ?> tag before the previous of previous node, and empty <?php after, but it make code keep working.

New Rector rule or cs tool may needed to clean the code for that :)