Flightradar24 has released a revised data set:
Metrojet 9268 Extended Mode-S Data Decoded | Flightradar24 Blog
Most important additions are GPS-derived groundspeed & vspeed. As before, there's rather sudden transition from business-as-normal at 04:13:14 to a 8000 fpm descent at 04:13:18, followed by a couple of phugoid oscillations (though still continuing to descend), and recording stops at 04:13:39 with vspeed of -26000 fpm and groundspeed of 47 knots.
For some reason, all timestamps have been shifted, so 04:13:18 in the new spreadsheet corresponds to 04:13:01 in the original spreadsheet.
Barometric altitude exhibits a small anomaly (a blast wave?) at 04:13:13.7 and then goes wild.
Even with the abnormal descent rate, the aircraft has not been overspeed at any time (combined horizontal+vertical speed never exceeded 410 knots).