This looks like a mechanical edit. Was it discussed anywhere?
I'm pretty familiar with the sort of edge cases that occur around lifecycle tags on tourism=information, and would suggest that diving in with level0 was only a sensible option if each individual occurrence had been checked beforehand.

Hello,
It looks like the merging of two bits of river to form osm.org/way/376669668 might have broken a couple of boundaries, since the southeastern part was part of the boundary and the northwestern part was not.
I've split the river again; hopefully that will fix things.

For info, I've extended osm.org/way/1378901507/history across the road here, as the Teesdale Way is signed across the road here.

(based on the imagery)

Hello, is
osm.org/way/22703714#map=19/53.397876/-1.432447
a separate bridge or a separate path on the bridge? I suspect that it'll need to be split where the bridge starts and ends and "layer=1" and "bridge=yes" added to the "bridge" bit.
Best Regards,
Andy

See also osm.org/changeset/171453477 and osm.org/changeset/172508645 .

Yes it has!

I've added an untagged way osm.org/way/1429277102 and added it back to each of the relations. This possibly wasn't the most efficient way of doing it, but it did work.
Unfortunately, the iD editor is not good at spotting gaps. You can use overpass to detect problems - see https://community.openstreetmap.org/t/finding-broken-relations-with-overpass/129031 - and you can also use Josm's validator to do the same thing: osm.org/user/SomeoneElse/diary/406398 .

There were 27 relations in total. I added them back piecemeal because other people were fixing other errors in the relations at the same time.
I've not commented on the changeset that introduced the gaps (osm.org/changeset/171781477 ) because it's their first change and it wouldn't be fair that their introduction to OSM was the mess of relations that is West Dublin.

Hello,
If osm.org/way/233317913/history has a sidewalk on both sides the normal tag for that would be something like "sidewalk=both". "footway=sidewalk" notmally means "this is actually a footway of some other road".
Would it be OK to change this to "sidewalk=both" (if that would be correct)?
Best Regards,
Andy

Hello,
Along with quite a few other relations, https://osm.mapki.com/history/relation/2267444 seems to have been broken by your edits in the last day or so.
Previously it looked like this:
https://overpass-turbo.eu/s/2beU
and now it looks like this:
https://overpass-turbo.eu/s/2beW
An easy way to check for gaps in relations is, for every relation that you edit, go to that relation's OSM page (you can click through from your changeset). Here that would be osm.org/relation/2267444#map=15/52.67545/-6.84360 - you can see (until somone comes along and fixes it) an obvious gap there.
Best Regards,
Andy

I think some of the separately mapped sidewalks in here are a bit incomplete - see for example osm.org/directions?engine=fossgis_valhalla_foot&route=53.634039%2C-2.815702%3B53.634007%2C-2.815523#map=19/53.634189/-2.814973 .
If it was me, I'd just use "sidewalk=left" or similar here; if you're going to use separately mapped sidewalks you need to make sure that you join everything up.
Best Regards,
Andy

After editing any paths involved in a hiking route relation (e.g. all the coastal ones!) it makes sense to check http://ra.osmsurround.org/analyzeRelation?relationId=77964&noCache=true&_noCache=on (where 77964 is the relation) so that it matches what is signed on the ground. There are obviously genuine duplications (high and low tide, whether paths across the ranges are open etc.) but there are some very dubious spurs still.

I've fixed a dodgy overlap at the north end of that which clearly didn't exist.
I've assumed that the inland path to osm.org/relation/77964 as I presume that that is where that is signed and routed now (my GPS traces here are from 8 years ago and may not be accurate any more).

Hello - it looks like this edit introduced a small spur to the Wales Coast Path - I've split osm.org/way/1390827060 so that hopefully it's contiguous again.

Hello,
It looks like osm.org/way/1379326419 had been accidentally missed from NCN4 - I've added it back.
Cheers,
Andy

The woodland at osm.org/way/148883959/history got deleted in this changeset. What were you trying to do?

Any idea what "building=s" is on osm.org/way/252175919#map=19/53.269303/-3.914435 ?

What sort of building is a "seb"? osm.org/way/1367284049 .

Hello,
Lots of the houses in this changeset are "building=semidetached_house100752" - I suspect that is a typo?
Regards,
Andy