Rotoscoping train windows

I am trying to mask two windows in a moving train so that lettering appears through the windows on a billboard as I pull into a station. The first window works well but when I apply the second mask it seems to stop the first mask working…any ideas? Thankyou …Keith

In the second Rotoscope effect set Alpha Operation to Add

Thanks berndmj, unfortunately didn’t seem to work but was ok when I set to ‘minimum’ no idea why but a result. Thanks…Keith