The ConversionHost#enable and #enable_queue methods are currently relying on symbolized params to work properly. However, the parameters are passed as strings from the ManageIQ REST API, so they could inadvertently be dropped if not symbolized first. To replicate, attempt to call either method with stringified params instead of symbols, possibly using the rest api.
https://github.com/ManageIQ/manageiq/pull/18336
Created conversion host via REST API to trigger #enable_queue method. Task message shows : Configuring a conversion_host: operation=enable resource=(name: env-rhv43-01.cfme2.lab.eng.rdu2.redhat.com type: ManageIQ::Providers::Redhat::InfraManager::Host id: 3) Verified in 5.11.0.11.20190625161125_392c61e