[[!getResources? &parents=`[[*id]]` &where=`{"template:=":8}` &tpl=`mytemplate`]]
This question has been answered by Bruno17. See the first response.
From your description, I'd say the problem is not with getResources, which if I'm understanding you, worked fine until you installed pdoTools. Since pdoTools is a replacement for getResources, I don't see why you'd need both.
That said, I can't think of any reason installing pdoTools would cause trouble with getResources unless you happened to have a collision on one of the default Tpl chunks (which you shouldn't be using), or you've created some other custom feature that's colliding with pdoTools.
&where=`{"template:=":"8"}`
Is that your exact, full getResources tab above?
Did you try this:
&where=`{"template:=":"8"}`
Interesting issue. Never have heard or seen an issue like that and can't think, what could cause it.
Any chance to get manager-access to an installation, where this happens?