Re: Brood comb on top bars
As it's drone comb I'm assuming your frames have been built using worker foundation.
So the bees feel they do not have as much drone comb as they want so build it wherever they can which includes the space between the boxes. If it was a foundationless hive meaning the bees would already have built all the drone comb they want the area between the boxes tends to stay a lot less built on.
Many beekeepers scrape all this burr comb off every time they open the hive, however the bees just build it back. Me, I tend to let them have it how they want, but once a year in spring I will scrape the bottom bars of the top brood box and top bars of bottom brood box, just as an annual clean up & to stop really strong type structures getting built that make box splitting difficult.
44 years, been commercial, outfits up to 4000 hives, now 120 hives and 200 nucs as a hobby, selling bees. T (mostly).