Strange issue with Text Preview shifting mark position

There is this strange thing I’ve been noticing with Text Preview. I’m trying to test mark attachments and for some reason in the first combination of a line, the mark positioning is shifted.

You’ll see in this simplified example that the vertical bar in the first combination is shifted to the right some while the rest are centered on the stem, as they should be.

How are you implementing mark positioning? Anchors, or manual feature code?

The base glyph has an anchor
Mark as an outline (no anchor)
Mark as comb with component and anchor.

Manually adding CCMP
example: sub yiwn-arm question-arm' by question-arm.comb;

Here is a screen recording showing the issue:
Screen Recording 2021-11-26 at (3.3 MB)text_preview_issue