Seafile can't create library saying it exists in spite of it doesn't

I’ve removed a library in Seafile, and tried to create it again, but I receive an error:
“Conflicting with existing library ‘BACKUP’, please choose a different folder.”

I’ve stopped seafile server and cleared outdated data with ./seaf-gc.sh, but it didn’t help.
What can I do to completely purge removed data?

Thanks.

In client logfile I get these errors:

[09/02/19 15:53:17] seaf-daemon.c(502): starting seafile client 7.0.2
[09/02/19 15:53:17] seaf-daemon.c(504): seafile source code version 28db7b1ab15bda5921e950375d6a6fd701719026
[09/02/19 15:53:17] seafile-session.c(382): client id = fd5f5dcc97699d44d2d8c86ae3*********d74, client_name = tc_1CSERVER
[09/02/19 15:53:17] repo-mgr.c(6226): Commit a4aff18f8855f992afdcf7f042c09c319c1e6085 is missing
[09/02/19 15:53:17] repo-mgr.c(6226): Commit eb11878a3e5ac42c4b7bf6f5babc286c9ec69868 is missing
[09/02/19 15:53:17] seaf-daemon.c(529): rpc server started.
[09/02/19 15:53:17] clone-mgr.c(718): Transition clone state for c85cf6ad from [init] to [check server].
[09/02/19 15:53:18] start to serve on pipe client
[09/02/19 15:53:18] start to serve on pipe client
[09/02/19 15:53:18] start to serve on pipe client
[09/02/19 15:53:18] start to serve on pipe client
[09/02/19 15:53:18] clone-mgr.c(735): Transition clone state for c85cf6ad from [check server] to [error]: check server.