Is it normal for this to cause the game to lock up for 10-30 seconds every time the tool gets used? Or am I having some kind of weird interaction with other mods?

Edit: I guess this is only happening in Sandbox mode. Seems fine in regular gameplay.

Well priority is not really a thing in Factorio and you can influence it indirectly only. So what this mod does for a work around is it scans everything in the selected area. then if the area has ghosts it scans all other ghosts on the surface, so that it can move the matching ghosts outside of the area to a different surface.

So if you have a lot of unfinished blueprints and you prioritize for example a few boilers, it scans every other ghost if it is a boiler as well to move it. I'm not sure why would it be worse in Sandbox tho.

I tested it in my bot megabase with 330 hours of gametime and it didn't seem to lag.

What might affect is how MANY ghosts you have, e.g. on a mega base (like mine) with tons of ghosts (reinforced concrete as a hard foundation) it might take some time to scan them all.

Yes, that affects it. When the selection contains ghosts, the mod first checks the selected area, then scans all entity ghosts on that same surface to find matching ghosts outside the selection and temporarily pause them.

I noticed there is one optimization I can probably make. The API supports filtering by ghost name, so I should be able to ask the API only for the selected ghost types instead of fetching every ghost and filtering them in Lua.