In case this helps someone else (and apologies if this is covered elsewhere):
I was having trouble with tags not being picked up and displayed in the cloud. I found a fix that worked for me.
If you have several layers of documents and find that the tags in the lower levels are not being added into the cloud then try this:
Open your TvTagCloud Snippet and find the section of code headed "// Get the subentities of the supplied parent"
Find the line that reads
$subDocs = $modx->getChildIds($parentDoc, 3);
As far as I can tell, the digit ’3’ means that only three layers of sub-pages are picked up by the cloud.
Edit to the digit to suit your site. For me, I needed to go down 10 layers of documents.:
$subDocs = $modx->getChildIds($parentDoc, 10);
All I know is that this worked for me. Please correct me if I am wrong in how all this works.
Leapy