It appears that vertical speed was really unstable after take-off and that it did not gain much altitude. Possibly a result of flaps and slats misconfiguration?
https://twitter.com/flightradar24/status/1104676048317362177...
https://twitter.com/flightradar24/status/1104676048317362177...
As a real world example https://en.wikipedia.org/wiki/Spanair_Flight_5022 but I guess the 737 has a better alarm