I shoot a compound bow. It's a center shoot bow with a dropaway rest. Can someone help me understand the problem with a arrow not flexing when it leaves the bow.
How can a arrow be too stiff for this bow. I have hard that over spined arrows are less forgiving and I don't understand how.

You answered your own question. Take your bow and arrows to a competent archery shop and asked the experts your question and be guided by them. You did not say if you are having trouble hitting your mark. One other thing, how do you know if your arrow is flexing when you are behind it when shooting? I never saw my arrows flexing when shooting. Every time I saw an arrow flexing when shot was when it was being filmed with a slow motion camera.

I guess it would be possible to be too stiff. However, with that being said, you stated yo have a center shot bow (almost all are these days) and you use a fall away rest. Therefore You don't have to worry about a shaft being too stiff. There is nothing contacting the shaft upon release.
Needed flex comes into play where the arrow needs to bend around the bow when shooting a recurve or longbow or over the rest when the rest is fixed. Note when shooting with fingers the shaft will flex left to right but when shooting with a release the shaft flexes up and down.
So basically what I am saying, with your set up, yo can shoot a really heavily spined arrow and not worry. The increased weight will give you better penetration. My set up is similar to yours and I always use and arrow spined one step up from recommended.