5000 threshold cache memory?

Hi,

We have a SharePoint site that keeps records of Annual leave that is requested via a PowerApp.  The App stopped working earlier this year as the 5000 threshold was reached in SP. Deleted old records and reduced the SP site to around 3000 records.

Recently the app stopped working again but the 5000 buffer was not reached.  I cleared done some more old records around 400 and the app started working again?

Is there another area within SP that records are stored such as a Cache?  Or is this an issue with the PowerApp

Any ideas, thoughts??