I found, early on, that two of my first four colonies were heavily propolised. At the time I thought it due to the strain, but changing the frame runners so that bee space was correct cured the problem (my new supers were OK, but the brood frames were awful).
The beekeeper had used nails as frame separators and there was no bee space under the frame lugs - so the bees propolised all the small spaces. Maybe you have a similar situation? Raising the runners a mm or two may be all it needs to avoid the problem? If there is less than a bee space under the lugs, the bees will seal off the gap.
The beekeeper had used nails as frame separators and there was no bee space under the frame lugs - so the bees propolised all the small spaces. Maybe you have a similar situation? Raising the runners a mm or two may be all it needs to avoid the problem? If there is less than a bee space under the lugs, the bees will seal off the gap.