
The basic volumes are used for location information, so that's no problem.
The general rules for semisolids:
* shouldn't be huge.
* must not touch any other semisolid brush (some workarounds are possible, by making a single brush out of many brushes).
* perfect for pillars (the map does have many pillars).
* can't be used when a subtraction is in the solid brush. That is, a semisolid can't have any holes.
* Having those rules in mind, and by turning pillars into semisolids should simplify the BSP in that level, since it does have many pillars.
* If a semisolid for some reason doesn't work, the editor can't tell you, but you'll see it when players can go through it. But when following the rules it should be safe.
* I wouldn't work around the BSP problem with the map, since the problem is still there, and you'll probably continue to get errors, such as players dying in that spot, or the typical hall of mirror effect. Just delete the subtracted brush you see on the right in the image I posted, and check if the problem is still there after a full build. If it goes away, try redoing the subtraction a bit different.
* Also, in Build Settings, disable path building temporarily, so you don't have to wait for bot paths to be rebuilt each time.
* Noticed another thing that also applies to the AnataWa map; the weaponbases uses the wrong static mesh textures because Epic Games messed up or something like that. Run the command NewPickupBases in the editor's console to correct it, although it didn't fix every weapon pickup in my map--so in that case, select the pickup properties, Display, and under Skins, select Empty.
* I'm sure that there are no options for letting the mover stand still while a player is on it, but it could probably be done using triggers, but then, if someone is frozen on the lift, the mover won't come down, and if the mover is the only route away from that place, the player is stuck.
Lots of mappers contribute articles to beyondunreal, where they document how they change the behaviour of things, like movers. Could be something that helps there.