I see this quite a lot actually, although not with the name of the snippet being blank. I think in your case, BobRay is probably correct but I think I'd still expect the name of the snippet being called to appear? Or, you have something in a template/chunk which is effectively causing [] to be rendered/parsed.
The errors I get are slightly more helpful:
/core/model/modx/modparser.class.php : 538) Could not find snippet with name #9.pagetitle.
There are many of these, with multiple resource IDs. My case is fastField related and my thinking is that it's something to do with the order or how MODX is parsing the template. I've traced it down to a Wayfinder chunk that contains the following:
<dt><a href="[[~[[UltimateParent? &topLevel=`2`]]]]">[[#[[UltimateParent? &topLevel=`2`]].pagetitle]]</a></dt>
The error isn't triggered 100% of the time though which makes me think that when it doesn't appear, the page (or chunk) is probably being pulled from cache. In either case, the chunk appears to render correctly (I'd expect the navigation label on the page to be missing if the snippet really couldn't be found).
I'm not a fan of hiding error messages but if anyone has a clue why this could be happening, it could help others. This error message was introduced after an upgrade to 2.6.0.