DBConnection.Holder.checkout deadlock?

Hello! Need help from Ecto experts!
I have a problem. I’m trying to test some cluster features of my app with ex_unit_clustered_case package. Local cluster starts successfully, but when I’m trying to call some Ecto Repo functions in slave node, Repo always returns error

    message: "connection not available and request was dropped from queue after 1333ms. You can configure how long requests wait in the queue using :queue_target and :queue_interval. See DBConnection.start_link/2 for more information"

I started to investigate what is happening on cluster nodes at this moment using observer tool and found interesting processes on top:

Can it be some deadlock in this receive expression?

Maybe you have an idea how to fix it?