Interpolation in exported instances

I am having trouble with points interpolating incorrectly when instances are exported directly from Glyphs to an OTF file. For example, accented versions of a letter will have some points shifted horizontally one unit different from the interpolation result of the base letter. Sometimes the entire glyph shifts over up to four units. Set widths are unaffected. This problem does not occur when I generate new .Glyphs files for instances using “Font > Generate Instances”, but I would really like to avoid doing that in a family of 28 fonts!

Has anyone else had and, hopefully, fixed this problem?

What version of Glyphs do you have and can you send the .glyphs file

What is your grid step setting? Does it happen with grid step =0? You can add it as custom parameter in the instance.