If this is the Shadowrun 5th Advanced sheet this is due to an inconsistency in the prior armor management. If you want to stop it you could either correct the data entries or simply go to the attributes and abilities tab and add the attribute "armormigration042021" and set it to true. (This wont migrate all legacy armor, but reimporting or manual entry can solve this) To correct the data entry you need to make sure that for every armorname[number] you got an armorrating[number], armorcapcity[number], armornotes[number] . To make sure Roll20 saves them it is best to write something in it. A fix that the character sheet handles that alone is already on github and a merge for it was requested on Tuesday or Wednesday
