Postgres Dump - Creating index never stops

Hello Experts,

we have created a postgres dump using this command: pg_dump pixabay | gzip > pixabay.gz

After restarting postgres (even with a new cluster) and creating a new database, postgres is hanging while extracting the dump: gunzip -c pixabay.gz | psql pixabay

The log file shows that the autovacuum task is running (almost) endless...

2017-07-12 18:05:50.822 CEST [19586] hans(at)pixabay LOG: duration: 1594.319 ms statement: CREATE INDEX photos_download_photo_id ON photos_download USING btree (photo_id);
2017-07-12 18:05:52.340 CEST [19586] hans(at)pixabay LOG: duration: 1517.955 ms statement: CREATE INDEX photos_download_user_id ON photos_download USING btree (user_id);
2017-07-12 18:05:52.355 CEST [19586] hans(at)pixabay LOG: duration: 14.954 ms statement: CREATE INDEX photos_editorschoice_created ON photos_editorschoice USING btree (created);
2017-07-12 18:05:52.367 CEST [19586] hans(at)pixabay LOG: duration: 11.609 ms statement: CREATE INDEX photos_indexphoto_created ON photos_indexphoto USING btree (created);
2017-07-12 20:34:58.943 CEST [19626] ERROR: canceling autovacuum task
2017-07-12 20:34:58.943 CEST [19626] CONTEXT: automatic analyze of table "pixabay.public.photos_photo"
2017-07-12 20:34:59.942 CEST [19586] hans(at)pixabay LOG: duration: 8947575.013 ms statement: CREATE INDEX photos_photo_approved_by_id ON photos_photo USING btree (approved_by_id);
2017-07-12 20:35:00.471 CEST [19586] hans(at)pixabay LOG: duration: 528.777 ms statement: CREATE INDEX photos_photo_approved_date ON photos_photo USING btree (approved_date);

What could cause this problem or how can we debug it?

We are running Postgres 9.4 / Ubuntu 16.04

Thanks, Hans