Ipad mini is stucking at apple logo with some digitizers

I had 6 ipad mini digitizer replacements with 6 success. I purchased the glass and digitizers wihout ic and home button flex. I am doing soldering under microscope. I have lot of experience about soldering. So first 6 repairs done with success. But 7th ended with disaster. Back light was gone since i didnt remove battery while disconnecting the LCD.

Ifixit answers helped me to fix backlight. I soldered the backlight fuse.

I have the backlight back.

But i figured out i have different problems to answer now.

I have 4 different digitizers in stock which is soldered by myself and tested previously on other ipad mini with positive results. Now if i use 2 of them on this particular ipad mini (backlight repaired one) it doesnt pass apple logo. It shuts down. The other 2 digitizer passes apple logo Works good on touch but acts weird after 1 minute especially when i try to close to frame.

Questions

1- why some digitizers (or ICs) doesnt pass apple logo and shuts down. Any similar experience.

2- does any short on ic soldering or home button soldering damage digitizer or ic. Is resoldering ok or i need a new digitizer and new IC.

3- why home button flex has 8 points solder. I know first one is ground and 2nd one is actual home button point. What are the rest functioning ? Is it doing anything on touch.

4- why my previously tested 4 digitizers failed on my last repair. Are there different ICs. Or different home button flex cables. Different type of ipad minis. Or different quality digitizers ? Any experience ?

7th repair failed. After 6 success. Customer is waiting for 1 week. I finally ordered a new digitizer whole assembly. Waiting for it and for your answers.

I dont want to quit reusing resoldering digitizer ICs..... Thanks