It is possible when trying to upgrade a VCF environment to 9.0 after having using the Brownfield import feature, that the following messages are seen in the UI/logs when trying to plan upgrade to a future release or running vLCM configure prechecks.
Log file: /var/log/vmware/vcf/lcm/lcm-debug.log
XXXX is not compatible with the target BOM. The following set of products are not compatible:ESX_HOST:YYYY. If you have Standalone Host(s), please follow https://knowledge.broadcom.com/external/TBD to upgrade/patch them out of band through vCenter Server.
OR
Target SDDC Manager version: XXXX is not compatible with the system. The following set of products on the system are not compatible:ESX_HOST:YYYY. If you have Standalone Host(s), please follow https://knowledge.broadcom.com/external/TBD to upgrade/patch them out of band through vCenter Server.
OR
Selected ESX cluster(s) are part of an NSX cluster with Standalone Host {0} that is a Transport Node in NSX. NSX Upgrade will not complete until those Standalone Hosts have been upgraded out of band through vCenter.
VCF 5.2, with 9.0 SDDC Manager
Standalone Hosts have been added out of band through vCenter to a VCF environment and imported/synced using the Brownfield import method. These could then be causing compatibility issues or causing the domain containing them to not be fully upgraded to 9.0 due to NSX DPO requiring them to be upgraded before NSX version change can happen.
Upgrade the Standalone Hosts out of band directly through vCenter to a version compatible with the target release version or to the target release version itself.