IPI installations can fail to find existing COS instances (during bringup for CAPI based installations - 4.19+, or during bootstrap destroy/cleanup processing). This lookup failure also causes two COS instances to be generated (with same name), as the first one cannot be found.

4.20

100% - although since pagination is involved, the order of returned instances matters, requiring specifically named clusters or COS instances to reproduce

    1. Create an excessive number of COS instances in an IBM Cloud account (say 40 to 50 or more)
    2. Run an IBM Cloud IPI build

level=fatal msg=error destroying bootstrap resources failed during the destroy bootstrap hook: failed retrieving cos instance for destroy bootstrap: COS Resource Not Found

time="2025-10-30T13:46:30-04:00" level=debug msg="checking for existing cos instance: pbalogh-cos27in-snvsr-cos"
time="2025-10-30T13:46:31-04:00" level=debug msg="creating cos instance: pbalogh-cos27in-snvsr-cos"
time="2025-10-30T13:46:35-04:00" level=debug msg="created cos instance: pbalogh-cos27in-snvsr-cos"
time="2025-10-30T13:46:35-04:00" level=debug msg="checking for existing cos bucket: pbalogh-cos27in-snvsr-vsi-image"
time="2025-10-30T13:46:35-04:00" level=debug msg="creating cos bucket: pbalogh-cos27in-snvsr-vsi-image"
time="2025-10-30T13:46:37-04:00" level=debug msg="created cos bucket: pbalogh-cos27in-snvsr-vsi-image" 

time="2025-10-30T14:07:15-04:00" level=debug msg="retrieved resource group id: 5e5ba1b22ec24020a2b0ce50b273eabb" time="2025-10-30T14:07:16-04:00" level=debug msg="creating cos instance: pbalogh-cos27in-snvsr-cos" time="2025-10-30T14:07:19-04:00" level=debug msg="created cos instance: pbalogh-cos27in-snvsr-cos" time="2025-10-30T14:07:19-04:00" level=debug msg="fetching cos instance for cluster: pbalogh-cos27in-snvsr-cos" time="2025-10-30T14:07:19-04:00" level=debug msg="creating cos bucket for bootstrap ignition config: pbalogh-cos27in-snvsr-bootstrap-ignition" time="2025-10-30T14:07:20-04:00" level=info msg="created cos bucket for bootstrap ignition config: pbalogh-cos27in-snvsr-cos/pbalogh-cos27in-snvsr-bootstrap-ignition" time="2025-10-30T14:07:20-04:00" level=debug msg="uploading bootstrap ignition config to bucket: pbalogh-cos27in-snvsr-bootstrap-ignition" time="2025-10-30T14:07:20-04:00" level=debug msg="bootstrap ignition config upload complete to pbalogh-cos27in-snvsr-cos/pbalogh-cos27in-snvsr-bootstrap-ignition/bootstrap.ign"

Successful IPI cluster creation, no duplicate COS instances during creation, no orphaned COS instances (from bootstrap resources)

This appears likely to only have been introduced during the migration to CAPI based IPI support, when the GetCOSInstanceByName was added (4.18+).
https://github.com/openshift/installer/blob/e064c5ffbac163a2d6999fe20273054ebfbafcb6/pkg/asset/installconfig/ibmcloud/client.go#L692-L711

This pagination may also affect COS Bucket lookup
https://github.com/openshift/installer/blob/e064c5ffbac163a2d6999fe20273054ebfbafcb6/pkg/asset/installconfig/ibmcloud/client.go#L645-L667

which might benefit from a fix too, if that is the case.

ResourceController API has very basic return content
https://github.com/IBM/platform-services-go-sdk/blob/7a608d80bbd7b6224ee5234b1a4e9afaba27aa23/resourcecontrollerv2/resource_controller_v2.go#L5007-L5017

But use of the Pager struct would be helpful
https://github.com/IBM/platform-services-go-sdk/blob/7a608d80bbd7b6224ee5234b1a4e9afaba27aa23/resourcecontrollerv2/resource_controller_v2.go#L5654-L5668
in place of the call to ListResourceInstancesWithContext