Upgrading Commerce: Migration failure on Serializable Cart. Upgrading from version 11.2.6 to version 13.3.1

The migration seems to be failing when trying to migrate the carts over to the new version.

3:31:05 PM: Completed migration step: Migrates existing serializable carts.

3:31:05 PM: Failed to migrate existing serializable carts: System.NullReferenceException: Object reference not set to an instance of an object. at EPiServer.Commerce.Serialization.Json.HashTableJsonConverter.ReadHashtableItem(JsonReader reader, Hashtable hashTable, JsonSerializer serializer) at EPiServer.Commerce.Serialization.Json.HashTableJsonConverter.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.DeserializeConvertable(JsonConverter converter, JsonReader reader, Type objectType, Object existingValue) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.ResolvePropertyAndCreatorValues(JsonObjectContract contract, JsonProperty containerProperty, JsonReader reader, Type objectType) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObjectUsingCreatorWithParameters(JsonReader reader, JsonObjectContract contract, JsonProperty containerProperty, ObjectConstructor`1 creator, String id) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent) at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType) at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings) at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSettings settings) at EPiServer.Commerce.Order.Internal.DataAccess.SerializableCartDB.CreateCarts(DataTable cartData) at EPiServer.Commerce.Order.Internal.DataAccess.SerializableCartDB.FindCarts(CartFilter cartFilter) at EPiServer.Commerce.Internal.Migration.Steps.MigrateExistingSerializableCartsStep.Execute(IProgressMessenger progressMessenger)

3:31:05 PM: Start migrating serializable carts...

3:31:05 PM: Starting migration step: Migrates existing serializable carts.

Has anyone had an issue like this? Is there any way to get more details on this error?