Thanks for reporting this issue!
At this stage the only advice I can offer is to stay away from groups and avoid using them.
Groups have always been problematic in Flash due to the way they were implemented by Macromedia.
Instead of groups, use a combination of Drawing Objects (Unions), Layers and Graphic Symbols, and you will have better flexibility and control; Find And Replace Strokes will also work fine.
We may try to explore this problem further for our future releases, but it is very low priority and I cannot promise anything at this stage.
In this foundational article from 2011 I have clearly written:
"Groups should be avoided at all times. Drawing objects (also called Unions) are a lot more flexible, but should only be used temporarily or with caution. The automated Find and Replace Color function in Flash 8 only works on raw vector shapes inside symbols. A typical problem during production may be the requirement to change some particular color in one particular character.
If groups and unions were not used the task becomes a simple automated operation. The finished scenes are subjected to a Find and Replace Color and in no time the problem is solved. On the contrary, if groups and unions were used during character creation, the operation snowballs and becomes a tedious time-consuming process, which requires manual operations and double-checking."
Good luck with your work!