Log in to the second user and run the system file checker. On the desktop screen take the mouse cursor to bottom left corner and right click, select Command Prompt (Admin). In the CMD window type sfc /scannow and press enter. Wait for it to finish the scan. It might show that it has fixed some errors and unable to fix others. Now either type exit and press enter or use the X top right to close. Reboot the PC and try the main user again.
OnePlus 5T review