Describe the bug
When we try to delete an investigation, we get the error message "This path does not exist."
The collection does not appear in the database or the redis cache.
We tried to delete it from the cli alephclient and curl, same error.
This investigation appears in https://aleph.example.com/investigations list though.

To Reproduce
Steps to reproduce the behavior:

1. Go to investigations
2. Click on an investigation
3. See error "This path does not exist."

or

curl -X DELETE "https://aleph.example.com/api/2/investigations/383"      -H "Authorization: ApiKey XXX" 
{"status": "error", "message": "This path does not exist."}

or

$alephclient --host https://aleph-aws.lemonde.fr --api-key XXX delete -f 383
Error: Collection does not exist.
$ alephclient --host https://aleph-aws.lemonde.fr --api-key XXX flush -f 383
Error: Collection does not exist.
$ alephclient --host https://aleph-aws.lemonde.fr --api-key XXX touch -f 383
Error: Collection does not exist.

Expected behavior
Web console: the option to delete the investigation and confirm
CLI or curl: deletion successful

Aleph version
4.0.2

Screenshots

Additional context
We migrated our aleph data to a new infra: elasticsearch, database, etc. and upgraded at the same time from version 3 to 4.0.2