I made uncooked freezer jam from berries in my yard.
I put the prepared jam in jars and screwed on the lids, being careful not to screw them on too tight with 1/2 headspace. After letting them sit on the counter for 24 hours for the pectin to set, the jam was seeping out of the lids and when I unscrewed the lid the jam oozed out.
I've made a lot of freezer jam and this has never occurred. To clarify, I used 6 cups crushed berries, 1 1/2 lemon, 4 c sugar, one cup corn syrup and 1 3/4 pack pectin.
Wow! I have not seen this before and I am very interested in what happened. The picture suggests that your pectin gelation kept expanding after you put it in the containers. How did you mix the powdered pectin with your recipe? Did you mix it with water and boil it first (there was no mention of water in your description)?
General guidelines for making jam at home
With any jam or jelly, pectin is the critical ingredient to get it to set. Pectin can be pretty finicky and requires the proper ratio of acid and sugar to set properly. Acid comes from the fruit itself and any extra acid you add (in this case lemon juice). Sugar comes from the fruit and from the sugar and corn syrup that you added. Here are the recommendations from the National Center for Home Food Preservation for using standard pectin.
They recommend 2 cups berries: 4 cups sugar: 1 pkg pectin (6 Tbsp): 1 cup water.
Following the recommendations on the pectin package should also result in a good quality product that sets properly. Adjusting these ratios often leads to a jam or jelly that won’t set or is too hard. Adding more acid can make the pectin unstable and it can “weep”. There are low-sugar and no-sugar pectins available and these would be recommended if you want to use less sugar than called for in the standard recipe.