Hi,
Apologies for the delay.
I attempted to figure out what change could have fixed this issue, but unfortunately I was unable to find a specific fix. Interestingly enough while looking at things, I checked out a commit that was 2 commits after the 5.5.4 release where it would be listed as 5.6, and it streams in the large static mesh fine even though those commits didn’t make any changes to any type of thing related to actor bounds, static meshes, or streaming in world partition.
Regardless, I created a bug report for this issue just in case and that can be tracked here if/when it’s approved for public visibility: Unreal Engine Issues and Bug Tracker (UE\-278445\).
There is no ETA as priorities for bugs and features can shift at any time.
Regards