Split level has precedence over allocation method, so if split level says a file belongs with other files on another disk, that is where they will go.
Also, most free is the least efficient allocation method.
I wonder if it's as simple as the "bluez-firmware: version 1.2" upgrade in 6.10.0-rc1 causing the issue as the NMBluezManager is a different version on the two logs you've attached?