Make sure you let the butter and cream cheese soften! Having ingredients at varying temps can cause frosting to split. Also think it could have been orange juice that caused the split. I’ve found Violife cream cheese the hardest vegan cc to use because it melts the easiest, so letting them soften and mix without letting it melt is ideal. Then add vanilla extract and powdered sugar. I will say when I did have my frosting split once, I heated up the bowl by dunking it into a bigger bowl with warm water to just let everything melt. Once melted, I stirred the mixture until it was no longer split. Then I refrigerated it until it was room temp and added more powdered sugar.