This discussion from 2021 is also relevant, however does not talk about the structure of air walls:
HB Color Rooms - Solar Gains are not shown when rooms have airwalls
I found an interesting work-around to abandon air walls and use “thin, opaque walls” instead, as explained by @chris
I’ll also just say: if you only need this for visualization purposes of solar gain, you can always just run the simulation using a paper thin opaque wall instead of an AirBoundary. The total incoming solar energy will still be the same whether you use the AirBoundary or an opaque wall. It’s just not going to distribute the solar beyond the paper thin opaque construction so some of the other load balance terms output from the simulation won’t be as accurate. But you can just run another simulation with AirBoundaries for that case.