One of the polygons in the Thailand admin boundary is not closed, thus not a valid boundary. The area that starts with the point 100.084653 20.352275 does not end with it, as it should. I have no experience with OSM, how to fix this?
There was at least a gap, a duplicated member in the relation (overlapping Way: 1040826674) and an outer boundary flagged ‘inner’, I hope I have fixed it.
But that was the land_area boundary, not the one you mentioned. I do not see any gap in the one you referred to.
well, I’ll investigate further and come back here, but that polygon seem to end with 100.0971103 20.3154431 and not 100.084653 20.352275, unlike all other polygons of existing countries that are self-closing.