Touch ID no longer working after screen replacement

I repair a lot of iPhones and am only ever having troubles with the 6 plus’s

generally what happens is i’ll do a screen replacement and when it comes to the home button it unclips from the flex cable with ease.. i’m not rough at all it.. fast forward and im now plugging the screen back on and bam it says touch ID is no longer working (regular home button return to home feature is fine.)

i then power the phone down and attempt to unplug the flex to then reseat it as perhaps it’s not seated correctly? i then find that the home button and the flex seem to be binded together and stuck very tight, its near impossible to then separate the two and i end up tearing either the home button or the shields flex cable trying to disconnect the two.

i’m just after some insight on firstly has anyone got any ideas on why my touch ID will not be working in the first place after a seemingly normal home button transfer has been carried out with no issues at all..

before i obviously tear the flex nothing has seemingly gone wrong, im very gentle and the flex and home button seemingly unclip so easily and i doubt ive damaged it at all. When reseating the home button its not as if im hammering the home buttons flex cable into the backplates flex cable.. im lightly pressing them together until you feel that 'click’ the exact same as the i6/6s/6sp etc..

i’m so lost on why sometimes the touch ID will be working after a screen replacement on a 6 plus and i do the exact same prodecure for the next 6 plus and its touch ID is now broken :(?

lastly - have you got any tips for separating the lcd shield back plates flex cable and the home buttons flex cable if they are now literally binded together without breaking one of them lol.

thank you