i guess this may have been said ?
when in a normal cruise the plane will all of a sudden drop to zero in speed then descend at a crazy rate , then go back to speed and strt climbing ? happens more than once.
i guess this a bug ?
I fly the A320 a lot and have not experienced this - it can be a bit unpredictable just after take off, but in cruise its pretty reliable in my experience.
If your speed is dropping to zero, you may be experiencing icing of the pitot probes. Make sure you have the window/probe heat switch on in the overhead panel. Probe and window heat are automatic on the real airplane, so you should not have to do this, but oh well…