Currently, when you navigate between the 4 bottom tabs, the app uses a sliding navigation where the next tab slides in from the right.
Animations serve as visual cues for the user's mental model of the app structure. A sliding animation implies that each tab is a child or a deeper section of the previous one.
This animation works well for drill-down navigation, where we are moving deeper into a nested structure (ex. tapping a book to go to a book detail view).
However, the bottom tab bar represents the distinct, high-level sections of the app that are not hierarchically related. When you use a sliding animation, you are implying a structure that does not exist.
I suggest using an instant switch animation on the bottom navigation bar. You can check many other apps to see that this is standard interaction design pattern.
Love the app! Thanks!