Opened writer document has acquired black shading over text since last closed

Sometimes when I open a writer document that looked normal and readable when I saved and closed it, I see dark black shading over all the keyed characters. I can go to the shading command and remove the shading, but does anyone know where this minor but puzzling problem can come from? I never keyed in this shading. It has happened more than twice, but not every time. I will need more time to gather information about the details of this problem, but I wonder if it is a recognized issue. It is possible that I changed Windows 11 to dark and back to light, but the document was saved in a different mode, and I am aware of the dark-light settings in Writer. But I can’t say I am highly familiar or practiced with them, being new to Libre Office.

Not AFAIK

Are you using a template that you made as default? Or are you using the factory default template?

Try and track down the problem:
In the document/template that this happened, click in a paragraph that had shown a shadow and press Ctrl+M to remove direct formatting. Does a shadow appear? If so, edit the style of the paragraph. Open the Styles pane of the Sidebar.

  1. Right click on the Default Paragraph Style and select Edit Style. In the dialogue that opens, select the Font Effects tab and untick Shadow if it is ticked. OK.
    If Shadow is unticked then
  2. Right click on the highlighted paragraph style (the paragraph that your cursor is in) and select Edit Style. In the dialogue that opens, select the Font Effects tab and untick Shadow if it is ticked. OK.
    If Shadow is unticked then
  3. Select Character styles pane (2nd icon from left with tooltip Character Styles). Right click on the highlighted Character style (the paragraph that your cursor is in) and select Edit Style. In the dialogue that opens, select the Font Effects tab and untick Shadow if it is ticked. OK.
    If Shadow is unticked then
  4. Select all the text, remove the shadow
  5. Save

Shadow is not set as a keyboard shortcut by default nor is it set in a default style. There is a possibility that corruption in the user profile is causing the issue but best to check the document first.