Can frontal lobe seizures be difficult to interpret on awake eeg? is that a reason to do a sleep eeg study?

Absolutely!: Frontal lobe seizures are notoriously hard to find on EEG. Sometimes they only come out to play at night. Sometimes the movement caused by the seizure totally obscures any EEG findings; the diagnosis becomes more apparent from the video/EEG than from the EEG alone, in my experience.

Sleep deprived EEG: When seizures are part of the diagnostic question, a sleep deprived EEG is the appropriate approach. The period between wakefulness and sleep is a fruitful period during which seizure discharges are seen. Before ambulatory EEG or other long term monitoring, the sleep deprived EEG should be done.