Why can't I migrate to a specific postgres database?

Question

I am currently evaluating if it makes sense to migrate my existing, self-hosted MariaDB database to a managed PostgreSQL database in the cloud. For this task I am using the tool pgloader version 3.6.9:

pgloader mysql://user:pw@localhost/mydb postgres://user:pw@external-server/mydb?sslmode=require

This works fine and I was able to copy all the data over to the new database. Now I created a new database in postgres via:

create database newdb
grant all privileges on database newdb to admin;

But migrating to this new database with the exact same command from above (only different db name):

pgloader mysql://user:pw@localhost/mydb postgres://user:pw@external-server/newdb?sslmode=require

is not working! I get the following error (IP address redacted):

Database error: end of file on #<CL+SSL::SSL-STREAM for #<FD-STREAM for "socket 1.2.3.4, peer: 1.2.3.4">>

I can only assume that there is a difference between the newly created database "newdb" and the old "mydb" which was created initially by the host provider.

Here's the output of \l on my postgres server:

                                           List of databases
    Name     |     Owner      | Encoding |  Collate   |   Ctype    |         Access privileges         
-------------+----------------+----------+------------+------------+-----------------------------------
 newdb       | admin          | UTF8     | en_US.UTF8 | en_US.UTF8 | =Tc/admin               +
             |                |          |            |            | admin=CTc/admin+
             |                |          |            |            | postgres=CTc/postgres

...


 mydb        | admin          | UTF8     | en_US.UTF8 | en_US.UTF8 | 

Only difference in my opinion here are the access privileges. Could this be the culprit? If so - what changes do I have to apply in order to be able to migrate to the newdb database?

Thanks for answers!