Whenever you load data with pg_restore or similar tools, run ANALYZE or VACUUM ANALYZE on your entire database to collect new statistics.
Without these operations, the database will not have up-to-date statistics on the tables and indexes, which may in turn lead to poor query plans.
This can also be the case after performing a major version upgrade since optimizer statistics are not transferred to the upgraded database.
For more details about ANALYZE, see the PostgreSQL documentation: https://www.postgresql.org/docs/current/static/sql-analyze.html