Hello Falah,
That’s strange. Products are not allowed to have the same band name twice.
I think that the problem happens before the Land-Sea-Mask. You could remove the last operators and check the output.
An option to work around is to save the graph and then edit the xml manually.
Btw., the I don’t use @marpet account anymore. Now I’m using this one.
See Farewell & Welcome SNAP Community