Indeed, before the update, the galItemThumb chunk was
<a href="[[+image]]" target="_blank" title="[[+description]]" rel="prettyPhoto[pp_gal]"[[+link_attributes]] class="screen" >
<img class="[[+imgCls]]" src="[[+thumbnail]]" title="[[+gallery.description]]" alt="[[+gallery.description]]" [[+image_attributes]] />
</a>
now, after the update the chunk is
<div class="[[+cls]]">
<a href="[[+linkToImage:if=`[[+linkToImage]]`:is=`1`:then=`[[+image_absolute]]`:else=`[[~[[*id]]?
&[[+imageGetParam]]=`[[+id]]`
&[[+albumRequestVar]]=`[[+album]]`
&[[+tagRequestVar]]=`[[+tag]]` ]]`]]" title="[[+name]]" [[+link_attributes]]>
<img class="[[+imgCls]]" src="[[+thumbnail]]" alt="[[+name]]" [[+image_attributes]] />
</a>
</div>
With this information, can you confirm that your guess is true? (I can’t because I don’t know the original galItemThumb chunk code.) If yes, does this mean the original implementer adapted in a way which is prone to update issues? Then I may find further, similar problems for other chunks and snippets?