i don't know if the standalone module works differently than isms' built-in switch. there can be some considerable lag when switching to software, as it depends on the app and host's re-detection speed of the grid. mlrv 2.6.1's serialosc interaction is particularly slow, and a little buggy. check out 1:04:
it takes quite awhile for mlrv to pickup the grid, and then the right half is broken. its LEDs do not turn off after the play marker moves past them, and this continues until about 1:31. it's fine switching back to earthsea, and then this time when i switch back to mlrv at 2:14, it's really quick, just like switching to a module. it restores the right half of the grid, too; the whole thing operates mostly normally.
i really think it just depends on the app. i noticed in sessions leading up to this that there would often be dud LEDs left on when switching to mlrv that couldn't be turned off, or mlrv would randomly turn on a few LEDs when starting up. also, if you look carefully at 2:25, mlrv has shifted everything left by one LED; hit button (6,5), and LED (5,5) started moving left. only switching to earthsea properly cleared and reset the grid, pulling up the correct LEDs on the left side.
workaround: avoid any timing-critical switches, which i didn't need to worry about in this ambient collage.