Updated firmware to 3.6 and SPRAYER parameters is missing now…
Will they be returned back?
It seems your pixhawk has 1M flash. Since 3.6 Sprayer is enabled only on Px4v3 FMU and later versions. (NuttX), with processors not affected by the 1M flash bug.
Your pixhawk is either an old one with processor affected or bootloader is old. Try update the bootloader to see…