It also appears that you change the data type for your stable var records. First question, does this canister carry production data? If so, you should think about a migration strategy that will be able to upgrade past stable data. If not, you better come up with a sound versioned strategy that will spare you from losing data in the future. E.g. a variant type that carries the version and a distinct type for each: { #v1 : [Job_v1]; #v2 : [Job] } or similar.