Will reinstalling deepin-desktop-environment fix this? Could it also be deepin's lightdm?

Do you try the latest system?

Before you make any change to grub config file, always backup the file to be changed. If you have backup, try restoring to original file, then update grub.cfg file, reboot and check.

Yes, it's on the latest system. Somehow, when it upgraded to 15.9, it broke something because it boots to splash screen and will stay there until the laptop's mouse is moved. When the laptop mouse is moved, it finishes boot and goes to the desktop.

grub config file keeps changing on it's own when laptop is rebooted even after update-grub. It's interesting to know that when it updates grub, the plymouth theme says,
"Generating grub configuration file ...
Found theme: /boot/grub/themes/deepin-fallback/theme.txt"
Normally, when it generates grub config update, the theme should be deepin/theme.txt and not deepin-fallback/theme.txt.
I also copied grub config from my working Deepin 15.9 laptop to my mom's laptop and update-grub. Also did not work since it automatically changes the grub file when it is rebooted.

Forgot to mention, also did grub2-mkconfig > /boot/grub2/grub.cfg in order to generate /boot/grub2/grub.cfg file.

This is the grub file on my laptop which works best.

# Written by com.deepin.daemon.Grub2
DEEPIN_GFXMODE_ADJUSTED = 1
GRUB_CMDLINE_LINUX = ""
GRUB_CMDLINE_LINUX_DEFAULT = "splash quiet"
GRUB_DEFAULT = saved
GRUB_DISTRIBUTOR = "` / usr / bin / lsb_release -d -s 2> / dev / null || echo Deepin` "
GRUB_GFXMODE = 1366x768
GRUB_THEME = "/ boot / grub / themes / deepin / theme.txt"
GRUB_TIMEOUT = 1

This is the grub file of my mother's laptop which has the problem ...

# Written by com.deepin.daemon.Grub2
DEEPIN_GFXMODE_DETECT = 2
GRUB_CMDLINE_LINUX = ""
GRUB_CMDLINE_LINUX_DEFAULT = "splash quiet"
GRUB_DEFAULT = saved
GRUB_DISTRIBUTOR = "` / usr / bin / lsb_release -d -s 2> / dev / null || echo Deepin` "
GRUB_GFXMODE=1366x768,1280x720,1152x768,1024x768,auto
GRUB_THEME = / boot / grub / themes / deepin-fallback / theme.txt
GRUB_TIMEOUT = 1
Why is the GRUB on her laptop different? Why does it fall into "deepin-fallback / theme.txt and not" deepin / theme.txt "? Another is the GRUB_GFXMODE, if I put it in 1366x768 or AUTO, it returns to the line of different resolutions that you are looking at. the laptop or AUTO, it does not fit me ... It keeps booting up to the Deepin logo and does not enter the desktop unless I move the mouse.

Yes. I lose my windows 7 partition after update(appesred as empty SD card no more Windows files)Restored Windows From Backup reinstalled Deepin and now everything works fine