I don't see your data or schemas so will just outline some generic steps to try:
1. Make sure that your two XDM Profile based schemas have exactly one primary identity marked, and if those two identities aren't in the same namespace, then at least one of those schemas must have a secondary identity that matches the other schema's primary identity.
2. Mark your datasets for profile service and then load your data. Marking afterwards doesn't work as loading profile service is not retroactive.
3. Go to the Profiles page and look at the union schema. Confirm that the union includes fields from each of your schemas.
4. On the Profiles page confirm that the default merge policy is still timestamp based and doesn't explicitly include or exclude datasets... default is "all" which is what you want.
5. On the Profiles page click the Find Profiles option. Enter an identity value that you know is in both or your datasets.
6. If you can't see your fields well enough to confirm that this profile has data from both datasets, then use the GET API call from Postman or equivalent.
7. If none of this works then open a Support ticket by clicking the "?" symbol in the upper right corner of the page.
-Kevin
