The voltage on Q1-C should move around at the LFO freq. If it's not, then the LFO is definitely stuck. Since it was working and now it's not, the most likely suspects are a bad solder joint & conductive debris. Inspect everything, especially around the SPEED pot, R17-R22, Q1, C11-C14. Use magnification and plenty of light. Have you removed & replaced any parts during the build?