You are using method 'MB' - Safety Stock (Time-Based Maintenance) in Product master, and set up safety stock in SNP planning book, everithing looks fine.
However you experience by running the Product View /SAPAPO/RRP3 that by some products no safety stock elements are visible.
What can cause this?
One possible reason could be that the Unit of Measurement (UoM) for the planning book is different than the UoM defined for the product in the product master, and there is no conversion rule maintained there.
By representing of the time based safety stock elements in RRP3 there is a call for unit conversion (/SAPAPO/DM_MAT_UNIT_CONV) this will return error if it can not convert the UoM to calculate the safety stock elements, so no safety stock elements will be shown.
This could be solved by setting same UoM for the planning book as it set for the product, or you create the unit conversion entry in the product master.