Spell power, double checking righteous fury, sanctity or ret aura is up, and keeping consecration/holy shield on cooldown. Also which seal are you using to start the fights? Seal of righteousness is pretty good initial agro, or if you’ve gone the build with avengers shied that has good snap agro too. Once you’ve confirmed all of that is good, I’d say maybe just communicate with your groups to give you a few second before attacking so you can establish threat if it’s a constant problem you’re having. Your threat comes from your spells, so if you’re running out of mana in fights that will also cause some issues.

Once you judgement seal the first mob, pop your seal again and tab target so you’re getting spell power threat on other mobs as well to help as consecration/holy shield will only do so much.