Help please - clutch depress weird issue

[G051999]

Hey folks. Hope someone can assist. 986 2002 S with 3 month old clutch and flywheel.

Intermittent issue that I experienced before and am now experiencing after new clutch/flywheel..

When I depress clutch and change gear, and all feels well, I hear and feel something spinning like it's supposed to (is this the flywheel or clutch? Apologies, not in any way a mechanic). Anyway on occasion, when I change gear, it's like nothing happens? The pedal feels a bit light, nothing seems to "spin" and the gear change is weird, sort of fast poppy and lumpy? Any ideas?

Thanks in advance