Our Aha instance has hundreds of products (potentially thousands) and each product has a large number of milestones.
When you build a report (Reports > Roadmaps > Epics) and try and select which milestone to show in the report, you have to scroll through a list of thousands of milestones to find the right one.
It's even worse on iOS, where the scrolling performance is so bad it makes it impossible to create these views on the go.
We quite often see people who want to report across multiple products, or want to include a release from another related product, so we can't limit the dropdown only to the current product.
That's a good first step, but it would be better if it only listed the milestones associated with the product so we don't have to think about this...
This is already in our short term backlog. We are switching the control for choosing milestones (usually called releases) so you can type a few letters and have the list narrowed to the relevant items.