Magnus Modulus weird issue

[Strategy]

I have now successfully built Magnus Modulus, a big'un

works EXCEPT! The LED's D2, D6 and D8 The first one is the tremolo LED, I believe the others indicate modulation (?) the LEDs are the only piece the documentation doesn't go into much detail about (understandably)

I can't get them to work. Correct resistors with them, ordinary LED's, even tried switching direction as the diagram is fuzzy on the direction of the negative side of the LED. I couldn't even find the modulation LEDs on the schematic to verify.

Any ideas what I should look for in trouble shooting this? I've tried a number of things and am mystified

Obvs. doesn't affect delay functionality but still an irksome lack of closure to the project

Help appreciated!!

Strategy