Glyphs hangs when deleting 567 instances from Font Info but deleting via Python is instant

I’ve made a small tool that makes it simple to generate a Glyphs “instance map” in a format that can be pasted into the Glyphs Font Info / Instances left pane:

Using the tool, I’ve added 7 x 9 x 9 = 567 instances to my Glyphs project:

When I go to the Font Info / Instances tab, select all instances and hit Delete, Glyphs 2.4.1 (942) hangs. But I can instantly delete the instances via Python:

while len( Glyphs.font.instances ) != 0:

Fixed it.