From the published chart the six "pings" before the 00:11 read on the chart at:
~18:25, ~18:28, 19:40, 20:40, 21:40 and 22:40. They are not every hour, as written everywhere:
In practical terms, I suspect that the 'pings' happened every 30 minutes, i.e. 11 and 41. My question would be, "Where are the missing 'pings'? Did they not fit the expected Doppler.
In relation to the 18:25 and 18:28 graphed points, there is no straight forward explanation, but may be the cockpit SatPhone has been used??