As other have mentioned, Ice and Water shield needs additional cover to protect from UV, manufacturer mentions 90 days for exposure so you will need to add something else to cover it.
The good news though since the PO failed to finish the job completely you can simply overlap the Ice and Water shield over top it's self anywhere the PO missed in order to fix the leak..
This is a case of the PO using the wrong material..
The correct material the PO should have used is a product called "Peel and Seal", it is the same base material as Ice and Water shield but has a top layer which IS designed for full UV exposure.
You can find it
HERE at Amazon..
You might be able to use the Peel and Seal over top of the Ice and Water Shield but you may want to contact thee manufacturer directly to find out for sure if it is compatible..
Peel and Seal was recommended to me by a RV dealer and so far it has held up to 4 yrs of outdoor exposure for us.