Consumption Plan Blade Contention Issue?

I am getting strange results with one function in particular on the consumption plan. I don't think it's a warm-up problem, because I can execute the function several times in a row, and some runs will be fine, and others ridiculously slow.
The function does nothing except query SQL Server (via EF) to retrieve an object (with associated sub-objects) and then map to a DTO (using Automapper). As you can see from the logs below response times are sometimes wildly different, for exactly the same function/object request 13-41ms for the first four requests, then 46,499ms for the fifth! These long ones seem to occur without rhyme nor reason, and cannot be due to load within my app, as the system is still in development, so I can only assume that the blade my app is running on gets overloaded.
Do I need to switch to the App Service Plan to get reliable execution times? I would rather continue to use the Consumption Plan to benefit from auto-scaling, etc.

2017-12-31T13:49:11.286 Function started (Id=c97e99e7-5543-4452-ac16-2b1611c132cc)
2017-12-31T13:49:11.286 EGift Info Basket requested eGiftId=59C05049-2057-4B48-9200-58BD2C5EDA0E
2017-12-31T13:49:11.286 Enter Get
2017-12-31T13:49:11.286 Got eGift id=59c05049-2057-4b48-9200-58bd2c5eda0e
2017-12-31T13:49:11.286 Forgery Check OK
2017-12-31T13:49:11.317 Mapped to DTO
2017-12-31T13:49:11.317 Function completed (Success, Id=c97e99e7-5543-4452-ac16-2b1611c132cc, Duration=41ms)
2017-12-31T13:49:24.030 Function started (Id=049be7f6-ce3f-41ec-8a71-3532517787d6)
2017-12-31T13:49:24.030 EGift Info Basket requested eGiftId=59C05049-2057-4B48-9200-58BD2C5EDA0E
2017-12-31T13:49:24.030 Enter Get
2017-12-31T13:49:24.042 Got eGift id=59c05049-2057-4b48-9200-58bd2c5eda0e
2017-12-31T13:49:24.042 Forgery Check OK
2017-12-31T13:49:24.059 Mapped to DTO
2017-12-31T13:49:24.059 Function completed (Success, Id=049be7f6-ce3f-41ec-8a71-3532517787d6, Duration=22ms)
2017-12-31T13:49:37.943 Function started (Id=8fc87561-f6ff-4c7d-a6f0-b59baade4175)
2017-12-31T13:49:37.943 EGift Info Basket requested eGiftId=59C05049-2057-4B48-9200-58BD2C5EDA0E
2017-12-31T13:49:37.943 Enter Get
2017-12-31T13:49:37.958 Got eGift id=59c05049-2057-4b48-9200-58bd2c5eda0e
2017-12-31T13:49:37.958 Forgery Check OK
2017-12-31T13:49:37.958 Mapped to DTO
2017-12-31T13:49:37.958 Function completed (Success, Id=8fc87561-f6ff-4c7d-a6f0-b59baade4175, Duration=13ms)
2017-12-31T13:49:59.198 Function started (Id=190fef4f-35ee-4546-a02b-d436cf0eae15)
2017-12-31T13:49:59.198 EGift Info Basket requested eGiftId=59C05049-2057-4B48-9200-58BD2C5EDA0E
2017-12-31T13:49:59.198 Enter Get
2017-12-31T13:49:59.198 Got eGift id=59c05049-2057-4b48-9200-58bd2c5eda0e
2017-12-31T13:49:59.198 Forgery Check OK
2017-12-31T13:49:59.220 Mapped to DTO
2017-12-31T13:49:59.220 Function completed (Success, Id=190fef4f-35ee-4546-a02b-d436cf0eae15, Duration=15ms)
2017-12-31T13:51:14.892 Function started (Id=2e4eede2-715a-45ae-b7dd-c5146dfc9953)
2017-12-31T13:51:15.607 EGift Info Basket requested eGiftId=59C05049-2057-4B48-9200-58BD2C5EDA0E
2017-12-31T13:51:19.170 Enter Get
2017-12-31T13:51:52.952 Got eGift id=59c05049-2057-4b48-9200-58bd2c5eda0e
2017-12-31T13:51:52.963 Forgery Check OK
2017-12-31T13:51:58.213 Mapped to DTO
2017-12-31T13:52:01.557 Function completed (Success, Id=2e4eede2-715a-45ae-b7dd-c5146dfc9953, Duration=46499ms)