Sudden drop in speed and altitude? Can someone tell me exactly what happened on this flight? It was a brief moment of sudden drop in altitude (6000 feets) almost at the same time with a drop on engine powers. It's a drop of signal from flightradar trackers or an issue recorded in flight? Thank you!

https://www.flightradar24.com/data/flights/w63655#20da042d
Smooth descent at 1500 feet per minute from 30,000 to 11,000.  Nothing unusual.
Or was there a blip somewhere in the data that I scrolled past?  (Where?)

Edit: The blip at 13:16 is from 36,000 to 29,600 and back, in less than a minute.  A 12,000 fpm dive followed by a 12,000 fpm climb (and vicious G force at the pull-up) is probably impossible for an A320-232.