But how does that relate to pitch ? - achieving a sweep with the existing steps on a pattern will take planning and slides or an LFO which is only trigged once etc

FWIW The reason I asked about voice share is that a Lock Trig on a subordinate track will mess about with the prime Track Voice in certain circumstances, so to keep it simple use non-shared-voice tracks first - there is a strong likelihood you are just forcing the default parameters of Track 3 to eclipse the Sound of Track 4 when the Lock trig is passed - it will interrupt T4 with T3 values

you’ll need to list steps to replicate in order to see what’s going on here