Using Virtual Master with Variable Font results in font not displaying in Webkit browsers

I’m currently experimenting with optical sizing for an icon font (with Glyphs 2.6.1). Because optical sizing is most important for just a couple icons, I’ve tried using Virtual Master. It appears to work in Firefox, but Chrome and Safari both refuse to render the icons that have optical size set on them with CSS.

Any icon without these axes set still works.

Edit: Taking font-variation-settings below 100 (the minimum for the axis) for optical size renders the icons as optical size 100. But going back up to 100 causes them to fail to render again. Going above 200 (the axis max) doesn’t trigger a successful render.

Edit 2 This is in Chrome 73.0.3683.75 and Safari 12.0.3.

There are several problems with the optical size axis in Safari. Variable font optical size issue

This was fixed in build 1220 by what I believe was always including the cvar table during the export.