Why is my OLED not working

I am trying to perfect digitiser repair on iWatch 4.

I have been successful in S2 and S3 . But for some reason, no matter how gently I treat these screens , they do not work after taking the digitiser off.

The LCD is not physically damaged. But the battery may have been still connected before disconnecting screen.

Are these screens more susceptible to static damage?. If so how the protect other than using a static mat? This is becoming a very expensive hobby/lesson.

I have seen several utube clips where screen is repaired with power still on