From your explanation, it appears you’re trying to break down your event counts by itemId. However, you’re facing an issue because the recently announced schema compatibility changes make it impossible as item-scoped dimensions like itemName are incompatible with event-scoped metrics like eventCount. Unfortunately, with these new changes, you might not be able to have the breakdown you desire without some modifications in your data tracking or analysis process.

You might need to adjust how you track these events, perhaps by incorporating information about itemId into a different parameter that is compatible with eventCount for analysis. Alternatively, you might need to reconsider the necessity of having a breakdown by itemId under these circumstances. Given the limitations of the new schema compatibility changes, you might find value in conducting a broader analysis of your event counts without such granularity. If you’re really having trouble, reaching out to Google Analytics’ support team or community forums might yield some insightful solutions.