Yes, I have not heard from them since the one survey I received last month,
But according to FAQ you only receive one to two invitations a mnth
I would not worry yet.
I've been doing Pinecone surveys for over 3 years - sometimes I go months without a survey - then I get two in a row - I just think it depends on what they are looking for. I really like them - they always pay & I've gotten to try out some pretty neat things!