Your LFO is going beyond the maximum range of the cutoff, leaving it open for that time.
For example, if you have a triangle LFO with depth 20, and the frequency is set to 117, once the cutoff reaches 127 it cannot go any higher… so for the time where the LFO is going to 11 and higher the cutoff remains unchanged until the LFO level comes back down below 10. The way to avoid this is to center the parameter in the middle of the LFO range. For example if I want the cutoff to vary between 90 and 127 with no “dead” time then I would set the depth to (127-90) / 2 = 18.5, so either 18 or 19. Then I would set the cutoff to 127 - 18 = 109.