Welcome to the wonderful world of quantitative health metrics research!
Realistically, there's really nothing you can do. You can, and should, contact the people responsible for the study here: https://www.hsph.harvard.edu/applewomenshealthstudy/
In many cases, when there is a 3rd party involved, it is difficult to determine who is at fault for a failure. Most people tend to blame Apple, even when Apple is clearly not involved. But in this case, this is, indeed, Apple's app that's crashing. Your best bet is to contact Harvard and complain. These kinds of crashes will probably cause you to be labelled an "outlier" and your data will probably be thrown out. All that Harvard probably knows is that you simply stopped participating. They need to know that they are losing participants not because of lack of interest, but because of poor software quality. Then they can take that to the vendor and complain.