The problematic duplication with chemlambda v2 of the lambda term \x.((\y.yy)(xx)), an example proposed by ishanpm. Sometimes it duplicates, sometimes it doesn't.

Alternatively you can see (here). the same duplication done with (hapax)
    (stops at max. number of nodes 256)

CODE:
MOL NOW:

MOL AFTER:

before:

chosen:

after: