It seems they rolled out a new shortcut. I noticed the change about a week ago. Rather than using Option + Shift + Arrow Key to select text a word at a time, it now will increase or decrease indentation of bullet points or other bulleted text left and right with the arrow keys. It however does not work the same as the Increase Indent or Decrease Indent keys as those keys will only indent the bulleted line and turn it into a sub-bullet point where the Option + Shift + Arrow Key moves the whole bulleted stack to the right or left.
This is an interesting new feature, but it's pretty much useless and it needs to be mapped to new hot keys rather than the already used Option + Shift + Arrow Key hotkeys for selecting text. I haven't found a place to control these types of hotkeys. For example, under View Settings, General, Accessibility, there are Keyboard Shortcuts and I can change them between Outlook and Gmail shortcuts, but these only work for editing messages, not editing text.