Lebanon has had 6 prime minister administrations over the last 10 years. On average, that’s a new prime minister every 1.6 years.
Considering that Najib Mikati took office in June 2011, his resignation is by no means extraordinary–at least statistically speaking.
More broadly, Lebanon has had 67 PM administrations over the last 87 years, meaning the average life span of a Lebanese PM’s term is about 1.3 years. This makes Mikati’s latest term slightly longer than average.