I see that you have opend multiple instances of the app in different tabs.
When changing the model and re-running the app, data in other tabs might cause conflict, since these were created using the old page.
Advise:
If you still have an error; your microflow has a bug.
Use the debugger to find it: https://academy.mendix.com/link/module/17/lecture/187/5.2-Using-the-Debugger