In Winter '20 sandbox, retrieval for custom metadata using wildcard is failing:
<types> <members>*</members> <name>CustomMetadata</name> </types>
Th error was:
INVALID_TYPE: sObject type 'some__sobject__mdt'
The same retrieve request works fine in Production because production has not been upgraded to Winter '20.
Anyone else experiences the same issue?
Further notes: I also found out that the listMetadata API call is also failing for Custom Metadata. So there is no way for us now to retrieve the list of Custom Metadata in the org. Seems to be quite a major bug.