With this font (I *think* it was Noto Sans Bengali), font has upem 769, and a glyph has advance of 520. In hb-ft, I'm asking FreeType for size 769/64.; the end result is the advance I get back from FreeType is 519 on some systems, but not others.
It's possible you already fixed this and the FreeType on the windows bots is old. Wanted to bring it up for your debugging enjoyment.