This bug seems to only affect older InDesign documents and graphic elements from them that were created before the update to 16.2.1. The bug can NOT be reproduced in completely new 16.2.1 documents with newly created elements!

What happens:
For example, if you create a circle with the dimensions 200X200mm and a 10mm thick outline, this results in a circle with the dimensions
210X210mm

But if you now change the contour orientation from center to inside, the dimensions change unproportionally in height:

Instead of 200 x 200 mm the circle becomes quasi
an "egg" 200 x 199.999 mm

If you now set the contour to 8mm, the element becomes proportional again.
However: if the contour orientation is now changed again from
"Aligned inside" to "Aligned outside", a conversion error happens again.

Instead of the dimensions 216 x 216 mm
the dimensions are now 216 x 215.999 mm.

In these cases, the dimensions cannot be corrected by direct input in the control palette or by clicking on the arrow keys!!!!!

If you enter 216 mm via direct input, 215.999 mm stubbornly appears.
If you click on the arrow keys, nothing happens in the height value! But if you change the width value now, if you have coupled the proportions (by means of the lock)
from 216 mm
to 216.001 mm
and with each desperate click further 216.002 mm;
and further. ...,003/...,004 !!!!

Very very annoying!!!!!!!! We are the BORG! Resistance is futile!

ATTENTION.
This rounding error also occurs with proportional scaling with the selection tool and can be transported via copy and paste even into completely new created InDesign(16.2.1) documents. Great. Or!?

As I said: In newly created documents with newly created graphics in Indesign 16.2.1 the bug cannot be reproduced. At least not so far ...

Unfortunately, this means for already existing documents from previous Indesign versions, - also because the bug can be scaled - , watch out like ****!

Keep your nerves! Even if it is colossally annoying!!!

Well! At least the other contour bug is fixed now.
Instead we have a new one!

Really super ...
is not this!

Translated with www.DeepL.com/Translator (free version)