Sometimes, cached data can lead to discrepancies between what's shown in the library and what's displayed in your mailings. Try clearing your browser's cache and then refreshing the page where you're viewing your mailings. This might help ensure that the latest asset versions are loaded.
Ensure that the mailings you're working on are correctly referencing the assets from the library. If the asset is still showing the old version, it might be because the mailing is still linked to the old version. Check the settings within your mailings to verify which asset version they're using.
Make sure that the assets you're replacing have the same naming convention and identifiers as the ones they're replacing. Dynamics 365 might use identifiers to link assets, so any discrepancies could lead to confusion.
Even if the asset in the library is replaced, you might need to manually update the content in your mailings to reflect the new asset version. Double-check that the asset references in your mailings point to the correct asset, especially if they're embedded or linked.
After making changes to your mailings, ensure that you're publishing or updating them appropriately. Sometimes, changes might not take effect until the updated mailing is published or reloaded.To troubleshoot further, you can create a new mailing and reference the updated asset to see if the issue persists. This can help isolate whether the issue is specific to the original mailing or a more general problem.