Tamil UU will not interpolate

I am working on a Tamil font and the vowel UU is not interpolating. Both masters have 102 nodes, and there are no other visible anomalies. The character has two components, and if I remove either one of them, the glyph becomes interpolatable.I ve tried way too long to fix this., is there anything obvious that I am missing? The same logic has worked for other weights, I have worked on a total of five masters. Please help.

how does it look if you activate the “Show Master Compatibility” in the View menu?

Thanks, thats a great option. It appears that node first was causing the issue, though I kept checking it for consistency many a times. I have no idea how it resolved itself now and not previously.

In the pictures, the start points are incompatible. Correct Path Direction (Cmd-Shift-R) fixes that in most cases. If it doesn’t, you can right-click on a node and choose Make Node First from the context menu.

More info in the Multiple Master tutorial: