Asalamualaykum, At my masjid I missed the main Jammah for Salat ul Isha, and the Tarweee Salah already started, but there was a second jammah going on in the back. I wasn`t sure what to do so I joined the taraweeh and combined my isha with it. After the prayer a Shaykh told me that was incorrect and what i should done was pray my isha with the jamat in the back. What was the right thing to do?

All praise be to Allah, and may his peace and blessings be on the last and best prophet and messenger, Muhammad.

What you have done is right. The second jama’at that was praying in the back should have not been started since we should pray with the main jama’at (congregation) of the masjid and only make a second jama’at if the main congregation of the masjid finished their prayers and are not expected to pray more. The regular/main congregation of the masjid that prays behind the regular imam should be respected, and people should not cause them disturbance.

Allah knows best.