Graph builder not working when reopened

snap
#1

I have made this graph builder and run it properly. I have saved this. When I reopened again it is not working. Following error is displayed. all the bandmath tabs are displaying to edit the equations.
java.lang.string cannot be cast to org.esa.snap.core.gpf.common.BandmathsOp$BandDescriptor

Looking for help. Thanking you.

#2

I’m not sure about the bandmaths error but, you need to have only one directed acyclic graph. Here you have two.
Two separate graphs will not work.