I have two masters. Exports as variable font without issues. The Variable Font Preview Plugin shows no sliders - only a small grey box under the preview.
I’ve tried to uninstall all other plugins without any result.
I’m using Glyphs 3151.
Does anybody experience this, and knows how to solve it?
Thanks 
Hi Nicolaj, You can solve this issue by using a newer version of Glyphs. Note that you can have multiple versions of glyphs in parallel. So keep your current version around (as a backup) and load a newer cutting edge that you can use until I have fixed that bug with older Glyphs versions.
Find all glyphs versions here
Sorry for the trouble, hope it helps. Good luck and let me know
Glad it helped. Thanks for letting me know.