WORKAROUND:
1.- First when importing from .tsv file for a user collection including its members, we are looking for two parts in the .tsv file. To get a sense of what this file looks like you can perform the "Export Collections..." operation:
Below is an example of the format of an import file that can be used to create a new user collection called "MyCollection" (first section) and add users to the collection (second section):
//--------------------
// User Collections
//--------------------
Name CollectionType QueryType Query AutoDefined Label Description SearchKey
MyCollection User None "" 0 Custom "" ""
//--------------------
// Collection Members
//--------------------
Name DisplayName UserID Address
MyCollection TUser1 TUser1 TUser1@DomainName.com
MyCollection TUser2 TUser2 TUser2@DomainName.com
MyCollection TUser3 TUser3 TUser3@DomainName.com
MyCollection TUser5 TUser5 TUser5@DomainName.com
Note: The "Name" column in the first section, "User collections", describes the name of the user collection you are creating or importing members into. The "Name" column in the second section, "Collection Members", describes the user collection name where the members should be imported into, and in this case, should match the user collection name specified in the "Name" column of the first section. Only the name of the collection and user's email address are required in the "Collection Members" section.
2.- Once the TSV file has been generated, issue command "Import-MNECollections -Path 'TSVFilePath'".
The command should execute and user collection being created with members imported.
Note: Using Excel to manipulate the TSV file for this process may add additional "tab" characters, which may cause errors during the import, such as, "...is not a valid Collection Tsv. Contains 1 of 2 sections. Ensure that all fields are tab-delimited and fields containing tabs or new-lines are surrounded by quotes" or, "Failed to import collection members: An item with the same key has already been added."