Yes it can happen, its rare, but it causes a severe eye infection called an endophthalmitis. So its not at all likely it was contaminated. Fluid is injected into the eye, the vitreous shifts and that alone can cause floaters. discuss your concerns with your ophthalmologist. These injections have saved the sight of millions of people worldwide
I am leaning toward thinking the avastin might have been contaminated, does this ever happen?
You may be noticing vitreous floaters in which case they do not absorb. They may however settle to the bottom of the eye where they are no longer visible. No way to predict the behavior of them.
will this resolve itself with time, or am I stuck with it?
Yes but you should still report it to your ophthalmologist. JCH MD