Multiclassing from Sorc to Paladin Seems to not give H.Armor Proficiency here in dndBeyond despite paladin having proficiencies in all armor. Is that in the rules or is it a bug?
That is the rule. Paladins and Fighters only get heavy armor proficiency if you take the class at character level 1. Clerics on the other hand can get it at any level provided the Domain you picked gets heavy armor proficiency.
Multiclassing from Sorc to Paladin Seems to not give H.Armor Proficiency here in dndBeyond despite paladin having proficiencies in all armor. Is that in the rules or is it a bug?
That is the rule. Paladins and Fighters only get heavy armor proficiency if you take the class at character level 1. Clerics on the other hand can get it at any level provided the Domain you picked gets heavy armor proficiency.
Yep, you don't get the new class's starting equipment, and only some of the starting proficiencies: https://www.dndbeyond.com/sources/phb/customization-options#Proficiencies