Martin,
Since f44ac12f1dcc, BG enablement is tracked with the LPFC_SLI3_BG_ENABLED bit, which is set in lpfc_get_cfgparam before lpfc_sli_config_sli_port() is called. The bit shouldn't be cleared before checking the feature. Based on problem analysis by David Bond.
Applied to 4.20/scsi-fixes, thanks!