One horizontal stroke in the character "脖" is too thin in 2.004 with fontconfig 2.10.4

[hexchain]

Prerequisites

• [x] If you are reporting an issue that affects glyphs for characters for a particular region or regions, did you verify that the characters are within the supported scope of the region or regions? This generally means GB 18030 or Tōngyòng Guīfàn Hànzìbiǎo (通用规范汉字表) for China, Big Five or CNS 11643 Planes 1 & 2 for Taiwan, HKSCS-2016 for Hong Kong, JIS X 0208, JIS X 0212, and JIS X 0213 for Japan, and KS X 1001 and KS X 1002 for Korea.
• [x] Did you thoroughly search the open and closed issues to avoid reporting a duplicate issue?
• [x] Did you go through the official font readme file to better understand the scope of the project, to include the Known Issues section at the very end?

Description

Similar to #285. One of the horizontal strokes in the character "脖" appears to be too thin in 12px, 14px and 15px:

% ftview -m "脖" -e unic 15 /usr/share/fonts/adobe-source-han-sans/SourceHanSansCN-Regular.otf

Other sizes do not appear to have this problem. Autohinting looks fine, too:

[punchcutter]

In the previous similar issue it was pretty clear that something got weird with the hints, but with this one I don't see anything quite as obvious so far.

[hexchain]

Looking from ftgrid, that stroke seems completely missing under 12-12.5, 13.5-15ppem:

That doesn't look correct to me, but I know nothing about glyphs, so this comment might be completely meaningless.