net-vips: Image.Thumbnail causes distortion on underlying file

I’ve been using NetVips successfully for many images, but a few have suddenly caused some weird distortions and I cannot understand why.

This is the original file

This is the thumbnail produced:

Here is the code

var expectedBytes = Image.Thumbnail("expected.jpg"), 320).WriteToBuffer(".png");
var thumbnail = Image.Thumbnail("input.jpg", 320);
thumbnail.WriteToFile("ouput/expected.png");
var actualBytes = File.ReadBytes("output/expected.png")

Assert.Equal(expectedBytes, actualBytes)

I tried both jpg and png (not sure if NetVips does anything different), but it always spits out this weird corrupted version. Yet windows viewer can open it fine.

Any ideas?