Thanks for the correction here!
I think I'm finished for today, and I will be offline Saturday and Sunday, so give yourself "free rein"!

This multipolygon was broken by having relations as members instead of ways, which is not defined for multipolygon - I've also corrected a similar error in other recent edits. Please check OSM Inspector (or another tool) when editing relations. Thanks!

Thanks - fixed.

Thanks - that's great, and it makes OSM Inspector (Areas) much happier!

What's the purpose of relation/15475169, which has only a single "inner" member that duplicates the tags of the relation? Something is clearly wrong there, but I'm not sure of the appropriate corrective action (and aerial photos don't clarify it for me).

This change has seriously broken the heath area relation (relation/13417952). Can you fix that?

Yes, that's exactly what I mean about ways that start off identical and then diverge. I've not used an editor that adds to multiple ways simultaneously - I didn't know that there are some that can do that. I'm certainly seeing unintended overlaps and gaps between areas. And also linear features that clearly ought to be the delineation between areas (fences, walls, hedges, etc) getting out of sync with their respective areas. I always understood it to be best practice to use these boundary ways to form the areas.
Having multiple ways sharing the same nodes certainly makes it very difficult to select the way you actually want to edit much of the time.

It's a judgement call whether the scrub is a single feature or not - feel free to separate into smaller relations if necessary.

The duplicated edges tend to fall out of sync when edited so that abutting areas end up overlapping or not quite meeting. This particular area was highlighted by OSM Inspector due to touching rings, so I fixed up some of its duplicated boundaries whilest editing.

Here's how I fixed the ones you introduced here:
changeset/130383971
The "inner" ways were present, but the relations were missing the "outer" way (the loch itself).

E.g. see the history of Loch Shiabhat:
relation/15013045/history

Ah, great. :)

Not sure what you mean there. Both of those stand alone and share no path with any other ways as far as I see. Which ways do you think duplicate them?

You seem to be creating relations that are missing their outer ways. I've fixed up dozens of them lately. Any idea what's causing that?

Thanks for fixing this before I spotted what I'd broken! :-)

Yes, identical coordinates, as reported on OSMInspector. 1 metre threshold, I think.

The main reason was the numerous duplicate points in the way. The easiest way to remove those was a simple Douglas-Peucker reduction.

Fixed - thanks

Ah, yes, that's more appropriate. Thanks for improving that.

It was marked proposed:highway=no, so I removed on that basis. Feel free to resurrect it if that was wrong!

Fixed that, and a few others I found in the area. Thanks for the correction.