I think I can add some info about a very similar issue we got.
On Neos 3.2.0 we are getting the following exception when we try to site:export a NodeType boolean property set (troe or false seems not to matter).
1 exceptions occurred during export. Please see the log for the full exceptions (including stack traces). The exception messages follow below: 0: Neos\Flow\Property\Exception Exception while property mapping for target type "string", at property path "": No converter found which can be used to convert from "boolean" to "string".
I saw this happens with several packages even with some not developed directly by us, therefore I think the problem is not in the package itlsef.