Rubin Sponar, the module designer, posted the following mods.

R2, R3: change from 100k to 110k for offset of Triangle output, also improves sine roundness.
R85, R92: change from 100k to 47/68k for better sine roundness. Adjust R81, R96 for amplitudes.
C20: replace with wire for a straight Pulse on VCO1.

I did the changes for R2, R3, and C20 as described above and used 68K for R85 and R92, and 270K for R81 and R96.

See also the original CubuSynth Engine post.

Comparison before and after of waveforms