Is this something you have added? I do not recall anything like that being included on the emonSD image although it has been discussed more than once.
(1) That rules out any mismatch of intervals causing excessive null data points and
(3) This confirms (1) and that it is not a Graphing/display anomoly
It is almost certainly not a time issue in this instance as the issue spans several days, although not impossible if the emonPi was to have had problems contacting the NTP server after some downtime. The browser time determines the default end time of the viewing window, so if the data was behind or perceived as behind due to a time mismatch you could see a similar output to your first screen grab.
Great.
[EDIT]
I have also replied to some of your points in the post above, back on your other thread Couple of questions about the SQL and Backups - #6 by pb66