Hello, There could be a number of factors, such as do you carb count? did you over calculated your insulin for the carbs you are eating? As you said, could be the hot weather and have you been more active than usual? Have you learned how to adjust insulin for your foods, activities/exercises etc? you could be insulin sensitive?
I'd like to add have you discussed this with your DSN for advice?
It is difficult to know why you are having hypos. As @MeiChanski explains, there are numerous reasons why they may be occurring.
I just want to check - you mention you have the Libre. Are you checking your hypos on with finger pricks. The reason I ask is that there are scenarios where the Libre can falsely report low readings such as when you apply pressure to the sensor which may happen when you are asleep. For this reason, I never trust hypos readings on my Libre.