Scott Ritter is a former US Marine Corps Officer and UN Weapons Inspector. He attempted to dispel the lies of the Bush Administration that were being used to justify the invasion of Iraq at the UN in 2003, eventually he resigned his position in protest. Today he is a fierce critic of the current US foreign policy and, informed by his knowledge and experience as a former military intelligence officer, he often gives his opinion on current geopolitical events in interviews to independent media outlets and in various online podcasts.

I followed his account as well much of his other content online and know from first hand experience that the topic he is always talking about is the current war in Ukraine, and his position on this war goes very strongly against the dominant pro-Ukraine narrative. His first ban has been confirmed to have been motivated by his remarks on the war and it is difficult to ascertain what caused his second ban (specially since Twitter doesn't allow you to see posts from banned people), but it is very difficult to see it coming from a different cause, specially since he did state on a recent podcast that he was again banned for his commentary on the war in Ukraine.

If you want to see for yourself what kind of commentary he was making, you can see an example on this interview:

https://youtu.be/r_FY87Se1d8