You could for example have a blueprint of an UFO flying at the top (or it could be invisible BP) moving left to right, and at random times changing its direction, then spawning the items under it to drop.
Instead of “tick” I would also recommend using “set timer by event” and set it looping. Or just launch the “drop object event” once, then have a delay of random float between range when finished spawning routine, then call the same event again.