I have run into this very bizarre behavior several times over the past year. I’ll get about halfway through a long (80–300 page) document, only for Word to suddenly start having all newly-created autoformatted lists of a particular type indent to four or so levels in (depending on the type). This has this occured with both numbered lists (created using 1.Space) and bulleted lists (created using -Space). When I manually un-indent an autoformatted numbered list back down to the first level, it does not start at 1; this suggests to me that Word is somehow trying to continue an earlier list (even though there may be many paragraphs of regular text between it and previous numbered lists, and my searches generally fail to find the previous list Word is trying to continue.)
Here is an example I created in one of the documents where I am experiencing this issue:

I would really appreciate help fixing this issue. While lists created using the ribbon button (for a numbered list: Home > Paragraph > Numbering) still work correctly, this is quite suboptimal; the documents in question are extremely list-heavy, so not being able to use a keyboard shortcut slows me down considerably.