Hi, first of all, i suggest you upgrade to Forest 5.4.0.
In the lastest releases we fixed a couple of bugs related with Corona, which would be causing this issue.
Regarding the license, render nodes don't fetch a license. But workstations does it, even if Forest objects are not edited. The license is used when Forest objects are edited or rendered, from an interactive Max session.
In any case, you can see who is using the license at any given time in the License Sever ("Computers" tab).
I hope that helps.