I've been playing on this world since late 2020 and it has worked perfectly fine up until now. I noticed that there are all of a sudden Pillager Outposts and what seem to be broken Mineshafts generating too, despite this being a standard Superflat with only Villages supposed to be generating.

The world file seems to be too large to attach here.

Sorry if this is formatted poorly, it's my first bug report.

Upon further review it also has been confirmed that this is not a bug.