People around him were puzzled by his erratic behavior.
Sporadic power outages often occur in this area.
断続的 means intermittent with on-and-off repetition, whereas 発作的 implies more unpredictable, seizure-like irregularity.
Compound of 発作 (ほっさ, 'spasm, fit, attack') + 的 (てき, '-like, -ic'). The word 発作 is itself composed of 発 (はつ, 'depart, emit') and 作 (さ, 'make, occur').