Apple Watch 3 overheating error after display replacement

Hello,

I needed to replace the OLED Display at an iWatch3 (GPS Cellular).

I did this before without problems. This time I get an error-symbol while initial charging.

It is the thermometer error symbol which is usually shown in the case of an overheating battery. The error symbol is shown immediately after plugging the watch to the charging cable. There is NO time for the watch to heat up.

Does anyone have any Tips what I may have done wrong? / What can I do better?

Thank you and Best Regards

Eric