Prettier 2.1.1
Playground link

--parser yaml

Input:

- foo: 0
  bar: 1

  # baz: 2
- quux: 3

Output:

- foo: 0
  bar: 1


  # baz: 2
- quux: 3

Expected behavior:

Prettier should preserve the single blank line, not add a second blank line.

I bisected this issue to commit ea84392 YAML: Preserve blank lines in comments (#8356). Cc @fisker.