I test it for many times, only one of them could delete success as we expected, changed rate:
How reproducible:
90%

We need to understand why the ServiceInstance didn't fully delete. Would someone reproduce this and supply the YAML for the ServiceInstance?

Paste the ASB logs for your reference:
[root@host-172-16-120-109 ~]# oc logs -f asb-3-6d7qc
...
[2018-03-13T08:22:36.607Z] [ERROR] - 100: Key not found (/service_instance/53946d4d-d572-4dab-adfe-7353f42884ed) [163]
[2018-03-13T08:22:36.607Z] [NOTICE] - 

[root@host-172-16-120-109 ~]# oc get serviceinstance -o yaml -n test | grep 53946d4d-d572-4dab-adfe-7353f42884ed
    externalID: 53946d4d-d572-4dab-adfe-7353f42884ed

Logs in comment 4 are the logs that display after `oc rollout latest dc/asb`. Just for your reference.

@Paul this is a broker bug.

PR: https://github.com/openshift/ansible-service-broker/pull/833

The ASB version: v1.1.16
[root@host-172-16-120-9 ~]# docker run --rm --entrypoint=asbd  brew-pulp-docker01.web.prod.ext.phx2.redhat.com:8888/openshift3/ose-ansible-service-broker:v3.9 --version
1.1.16

Service catalog version: v0.1.9
[root@host-172-16-120-9 ~]# docker run --rm --entrypoint=service-catalog  brew-pulp-docker01.web.prod.ext.phx2.redhat.com:8888/openshift3/ose-service-catalog:v3.9 --version
v0.1.9

Test steps as the description show and I test it for 7 times, all of the target projects can be deleted as expected! LGTM. Thanks all!

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2018:2013