What about Ahmadis/Qadianis? I think their salaat is also 100% same (per my knowledge) as of Sunnis, can we offer salaat behind them as well?
In Pakistan, perhaps after the emergence of Sipah-e-Sahaba, many scholars (not-affiliated with SSP) formed opinion that Sunnis can’t pray behind a Shia, though one of big moulanas (Noorani or Fazalur Rehman) prayed behind a big congregation but later on it was said that it was just to promote “peace”.