These are two different tenses, both in the passive voice.
"Ha sido + past participle" has the equivalent in English:
Has been/was + past participle
"Ha estado siendo + participle" doesn't have an exact equivalent in English as this would be the literal translation and it wouldn't be correct in English: "he has been "being" observed", but we can say in Spanish "Él ha estado siendo vigilado". Here we add the progressive aspect to the more simple "El ha sido vigilado" (He has been/was watched).
I hope this helps.
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