the recovery/reserved partitions are automatically detected and should be set in the “fixed” partition list. Chances are, it would seem, that this didn’t get set for some reason? It looks at the label’s that windows typically defines. If the recovery/reserved was setup as a custom partition, most likely the label didn’t get applied as would happen in a “default” scenario?
You should be able to correct this behaviour by adding the partition number to the fixed partition file. For windows 10, I believe the partition number used for recovery|reserved is number 3.
Resizable partitions use the filesystem volume to determine if it’s viable for resize. Windows reserved/recovery from at least windows 7 on typically has this as an NTFS partition.