Everytime I enter an expense using the QB app, it tells me "one of the items associated with this entity is no longer valid" but when I cancel and re enter it works fine?

Hello there, @Samanvaya. I appreciate for taking the initiative to troubleshoot the issue. I can share more information on how to fix data issues in QuickBooks Online (QBO) App.

The uninstall-reinstall process is the last resort we can share. This time, I recommend contacting our Customer Care Team since you've already troubleshoot it. They have the tools to look further is there are any open investigations about the error. 

While waiting for the fix, I suggest logging into QBO via browser to avoid getting this error. 

Here's how to contact them:

1. Go to Help, enter your concern in the search box.
2. Input Talk to a human.
3. Choose Message an agent.

I've included this article that you can use in your future tasks with QBO: Reconcile an account in QuickBooks. It contains the step-by-step process for zero reconciliation issues.

If you have other concern with QBO or the workaround I've mentioned, post here again. I'm always here to help you further. Have a good one!