Old topic, but encountered same problem in Nextcloud 14 after moving (not shared) directory from one user home dir into another.
Solution is to change in database, oc_share table.
select * from oc_share where file_target like '/Your AlreadyShared Share What Seems to Be Lost Now%';
See uid_owner and uid_initiator is changed to new user (instead of old, what it should be).
For me it was needed to be “admin”, so I’ve changed it:
update oc_share set uid_initiator='admin' where id=73;
UPDATE 1
nextcloud=# update oc_share set uid_initiator='admin' where id=5;
UPDATE 1