All names (unplaced or not) in POWO have been reviewed.
It is not always a nomenclatural problem.
See : https://powo.science.kew.org/about-wcvp#unplacednames
Most of the time, it is :
no correct name is available in an accepted genus
and I think this is the case with Philodendron imbe.
These names should not be deactivated : the concept is good, it’s just the name that is not the good name.
The iNat flagging of unplaced names is not intended to identify names that need to be inactivated, but to draw attention to the need of change of the name. I have seen many cases where some inatters have provided a publication that allowed a feedback to be sent to POWO and POWO un-unplaced the name (and POWO can’t see all publications).