Hello Razvan,
Welcome at this forum

Thank you very much for your report and congrats to The World's 3rd EM1022
(AFAIK) again!

For others:
1N400x as D2 never worked well for me either, if you would build it, start with 1N4148 there.
Changing R1 to 100k and adding filtering cap 150p was my idea (stolen from modern DEM) how to try to fight with (most probably) AM radio interferences (leading to "UFO" sounds caused by heterodining with clock frequency):

But Razvan has got rid of those interferences already by using optional clock buffer (which honestly does not make much sence to me, but maybe it was just eliminated thanks to changed wiring or something), which he has wired before R1/Cf mod, so we don't know how useful R1/Cf mod is..
T.