When working with 6 axes, the behavior involving setting instance values appears buggy.
I am having trouble pinpointing the exact problematic behavior as it seems to be inconsistent. A problem that I commonly experience is if I type in a value for the 6th axis, go to a different instance, and then click back onto the original instance, the value remains unchanged. I have noticed however, that the value of the 6th axis changes properly when that value does not match 3 other axis values.
I’m running Glyphs on MacOS High Sierra 10.13.6 and have gotten the same behavior in both 2.5.1 and 2.5.2(1179).