Flightradar24 has released a revised data set
Metrojet 9268 Extended Mode-S Data Decoded | Flightradar24 Blog
Most important additions are GPS-derived groundspeed & vspeed.
Hmm, reading through the FR24 blog, they say all pressure data (pressure altitude, TAS, vertical speed) are unreliable right after the "event" around 04:13:13 UTC or 331 seconds into the published FR24 data.
If we plot again the data including the new GPS computed GS and VS, to my eyes at least still only very limited conclusions can be made:
(Altitude data up to about the 347 second mark is from pressure altitude. Raw GPS-derived altitude is substituted afterwards with no attempt to match them).
After the event at 331 seconds, the GPS Vertical Speed remains negative until the end of data, averaging about -10,000 fpm. So that "zoom climb" reflected from the pressure altitude probably didn't actually happen.
That likely also means there's no real "phugoid" motion where the aircraft periodically regains some altitude before dropping again. But there are periods where the descent slowed down.
The TAS remain fixed at a few values throughout, so it is probably garbage past 331 seconds.