Ijtima,eid

Assalamu Alaikum. There are amongst us a group of people who actively sabotage the sunnah of Rasullullah (S.A.W) on the occasion of every Eid. They perform Eid Salaah right next to the Eid Gha in a Masjid, and usually time it so that their Eid salaah ends before the salaat at the eid gha. I am very sceptical of attending any gatherings hosted at this masjid. Could Muftiesab please explain what an Islahi ijtima is, and what the difference between this ijtima and what some people have recently referred to as the “Tablighi” ijtima.

I will understand if Muftiesab does not want to answer this question on the website, so if Muftiesab wants to answer me directly, i will also appreciate this.