There is always a risk of reflow when changing versions, and it isn't surprising if it happens for a dot release when one of the things modified is the text engine.
If you click in a paragraph and go to the Paragraph panel menu, you can choose Adobe Single Line Composer. That will prevent lines from re-wrapping when you change versions. The default setting is Adobe Paragraph Composer, which usually does a better job of composing paragraphs, but can change with version upgrades.
Not true, if a bug came up in a previous version and this bug is repaired you will see text recomposing also if you use the single line composer. There have been several bugs in the past according dictionaries and hyphenation. I would be very glad, if Adobe could repair them soon or has it done. Which would cause a wanted recomposition.
There are several reasons why it could recompose. Maybe that a font has been missed on the first place, maybe that you have used a user dictionary which is not available any more, or you have changed from the document settings to the computer's settings, maybe that you have updated the font, same name but a different version, maybe a linked file was updated with a different wrap setting or a different clipping path which has been used for wrapping.
As long as we don't have further information, we can only guess.
All of that is true in #3 post and I'm not advocating single line composer. but if the type recomposes because Adobe has changed the text engine, it is less likely to happen with single line composer.