AdvanceWidthMax mismatch


I submitted my new font to Adobe, and got a response that two weights cause an error:

Maxadvancewidth: AdvanceWidthMax mismatch: expected 1000 (from hmtx); got 970 (from hhea)

They asked to fix this, but I have no idea what could be the reason of this error. It occures only with Hairline and Hairline Italic. These weights have custom param weightClass:50, and this is the only difference.