"Force HDD Standby" has been removed from the SMART configuration UI.
Unfortunately, this settings is still use during disk temperature read. The setting present on individual drive has no effect.
See here for individual disk temperature read. In this line, "powermode" comes from the global SMART configuration, not individual drive configuration.
As a consequence, some drives won't go to sleep, or if they do, will be awaken on the next SMART temperature read.
Keep in mind that this bug will probably only manifest itself on a brand new install. The UI has been removed, but the value itself is kept from previous installation. So if you're coming from an old release, you might have the "STANDBY" value set in there.
I provided a script that set the value using the API and fix the issue here. Since then, my drives do to sleep as intended.
Please revert the change that removed that UI checkbox, or use the per drive setting when doing SMART temperature read.