LED flashed red once when power cable connected after replacing screen

I dropped my ASUS Zenfone 3 Deluxe (ZS570KL) and the screen is damaged. I can connect power cable and the LED show green light, indicating that it’s fully charged.

I RMA it to ASUS and they said there’s no screen replacement. So I sent it to a 3rd party repair shop. They said the screen part is 3rd party made and need preorder, so I left the phone at the shop.

6 days passed and they called me that the screen part is sent to the shop, however, they said the phone went into infinite power loop after replacement, they thought the board is defect and restored and returned my phone without cost.

I connected the phone with power cable, and it vibrate 0.1 second, then the red LED flashed once. It repeated the actions above every 10~30 seconds, until I removed the cable. Seems worse then before.

Why the hehavier changed(green light on -> red light flashed once)? What does it mean?