The issue seems to be arising from trying to incorporate an aggregated field with a pre-aggregated field as QuickSight does not allow you to handle scenarios like these.
Here are a couple helpful articles that dive deeper into scenarios where mismatched aggregations arise:
I’d suggest to review these and see if it helps diagnose your issue; if you have any additional questions, it may be easier to assist further if you’re able to create an anonymized copy of your dataset and upload the analysis to QuickSight Arena so that we can test out various work arounds.