macOS Mojave 10.14.5
Illustrator 23.0.6 - ( issue has existed through many versions / upgrades )
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I thought that I had successfully reported this particular issue in the recent past, but cannot find it in a search, so am re-reporting. My apologizes if I'm doubling up.

The Process :

Let's say I have multiple objects of various width and height sizes — e.g. to keep things simple, let's say one object is 4in w x 4in h, and another is 6in w x 4in h.

I then position/possibly-resize the multiple objects precisely and group them together so that their resulting total group's width and height is either non-fractional, positive integers — e.g. 12in w x 4in h — or systematic, fractional numbers — e.g. 12.25in w x 4.25in h … at times using a separate, deleted-after-use "shim" vector shape at the exact size I want the total group to be, to align (not snap-to) the multiple objects to.

After checking that the total group is the exact size that I want, I then (with any "shims" removed) upsize or downsize the group incrementally — e.g. say, by 1.5x, 2x, 3x etc.

The Problem :

In many instances, this upsizing or downsizing has unexpected/unintended results — e.g. upsizing a group sized 12in w x 4in h by 2x, should yield a result of 24in w x 8in h, but in my experience, may yield something like 24.0001in w x 7.9998in h. Many times the size discrepancies will remain but change slightly, if I attempt to start-over and re-do my steps.

Despite these types of size discrepancies not being optically discernable, it can be very frustrating, especially in instances where another designer or vendor I am needing to share files with, is planning to be able to precisely scale things up and down.

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bp