check your data dictionary stats
how many tables are you loading? you could try adding a filter, but i doubt that's the issue
It's a large but not ridiculous number of tables:
select count(*) from user_tables;
I'd gathered stats with the following before I asked the Q:
But lastly I did:
And after this it's happy again! I'm not convinced that I can explain why, but I'll do some more reading on all of the above.
Hurrah. I feel bad now for blaming SQL Developer :-)
Don't feel bad. We're very often just the messenger delivering the bad news.
We hit the data dictionary HARD. So stale/missing stats there often shows up as taking very long times to do things in the UI.