I can’t reproduce the effect. I think it must be down totally to the Feed Interval.
I’ve used Message Count of my emonPiCM reporting every 4.9 s, with Feed Intervals of 10 s.
OK, MessageCount.hours has no physical meaning, but I think it’s the same maths. 
Input processes:
Graph:
CSV Output:. The nulls at the start and end are where the graph doesn’t fill the window:
“Unix timestamp”, “emonpiCM_5:Msg”, “emonpiCM_5:Mh”
1700491400, 64613, null
1700491410, 64615, 0.1
1700491420, 64617, 0.3
1700491430, 64619, 0.4
1700491440, 64621, 0.6
1700491450, 64623, 0.8
1700491460, 64625, 1.0
1700491470, 64627, 1.1
1700491480, 64629, 1.4
1700491490, 64632, 1.6
1700491500, 64634, 1.7
1700491510, 64636, 1.9
1700491520, 64638, 2.1
1700491530, 64640, 2.3
1700491540, 64642, 2.4
1700491550, 64644, 2.6
1700491560, 64646, 2.8
1700491570, 64648, 3.0
1700491580, 64650, 3.1
1700491590, 64652, 3.3
1700491600, 64654, 3.5
1700491610, 64656, 3.6
1700491620, 64658, 3.8
1700491630, 64660, 4.1
1700491640, 64663, 4.3
1700491650, 64665, 4.4
1700491660, 64667, 4.6
1700491670, 64669, 4.8
1700491680, 64671, 5.0
1700491690, 64673, 5.1
1700491700, 64675, 5.3
1700491710, 64677, 5.5
1700491720, 64679, 5.7
1700491730, 64681, 5.8
1700491740, 64683, 6.0
1700491750, 64685, 6.2
1700491760, 64687, 6.4
1700491770, 64689, 6.5
1700491780, 64691, 6.7
1700491790, 64693, 6.9
1700491800, 64695, 7.1
1700491810, 64698, 7.3
1700491820, 64700, 7.5
1700491830, 64702, 7.7
1700491840, 64704, 7.8
1700491850, 64706, 8.0
1700491860, 64708, 8.2
1700491870, 64710, 8.4
1700491880, 64712, 8.5
1700491890, 64714, 8.7
1700491900, 64716, 8.9
1700491910, 64718, 9.1
1700491920, 64720, 9.2
1700491930, 64722, 9.4
1700491940, 64724, 9.6
1700491950, 64726, 9.8
1700491960, 64728, 9.9
1700491970, 64731, 10.2
1700491980, 64733, 10.4
1700491990, 64735, 10.5
1700492000, 64737, 10.7
1700492010, 64739, 10.9
1700492020, 64741, 11.1
1700492030, 64743, 11.2
1700492040, 64745, 11.4
1700492050, 64747, 11.6
1700492060, 64749, 11.8
1700492070, 64751, 11.9
1700492080, 64753, 12.1
1700492090, 64755, 12.3
1700492100, 64757, 12.5
1700492110, 64759, 12.6
1700492120, 64761, 12.8
1700492130, 64764, 13.1
1700492140, 64766, 13.2
1700492150, 64768, 13.4
1700492160, 64770, 13.6
1700492170, 64772, 13.8
1700492180, 64774, 13.9
1700492190, 64776, 14.1
1700492200, 64778, 14.3
1700492210, 64780, 14.5
1700492220, 64782, 14.6
1700492230, 64784, 14.8
1700492240, 64786, 15.0
1700492250, 64788, 15.2
1700492260, 64790, 15.2
1700492270, 64793, 15.5
1700492280, 64796, 15.8
1700492290, 64798, 15.9
1700492300, 64800, 16.1
1700492310, 64802, 16.3
1700492320, 64804, 16.5
1700492330, 64806, 16.6
1700492340, 64808, 16.8
1700492350, 64810, 17.0
1700492360, 64812, 17.2
1700492370, 64814, 17.3
1700492380, 64816, 17.5
1700492390, 64818, 17.7
1700492400, 64820, 17.9
1700492410, 64822, 18.0
1700492420, 64824, 18.2
1700492430, 64826, 18.4
1700492440, 64828, 18.6
1700492450, 64831, 18.8
1700492460, 64833, 19.0
1700492470, 64835, 19.2
1700492480, 64837, 19.3
1700492490, 64839, 19.5
1700492500, 64841, 19.7
1700492510, 64843, 19.9
1700492520, 64845, 20.0
1700492530, null, null
1700492540, null, null
So then I repeated it with Feed Intervals of 5 s - still exactly the same, no intervening NULLs.
“Unix timestamp”, “emonpiCM_5:Msg2”, “emonpiCM_5:Msg2h”
1700492935, 64930, 0.0
1700492940, 64931, 0.1
1700492945, 64932, 0.2
1700492950, 64933, 0.3
1700492955, 64934, 0.4
1700492960, 64935, 0.5
1700492965, 64936, 0.5
1700492970, 64937, 0.6
1700492975, 64938, 0.7
1700492980, 64939, 0.8
1700492985, 64940, 0.9
1700492990, 64941, 1.0
1700492995, 64942, 1.1
1700493000, 64943, 1.1
1700493005, 64944, 1.2
1700493010, 64945, 1.3
1700493015, 64946, 1.4
1700493020, 64947, 1.5
1700493025, 64948, 1.6
1700493030, 64949, 1.7
1700493035, 64950, 1.7
1700493040, 64951, 1.8
1700493045, 64952, 1.9
1700493050, 64953, 2.0
1700493055, 64954, 2.1
1700493060, 64955, 2.2
1700493065, 64956, 2.3
1700493070, 64957, 2.4
1700493075, 64958, 2.5
1700493080, 64959, 2.5
1700493085, 64960, 2.6
1700493090, 64961, 2.7
1700493095, 64962, 2.8
1700493100, 64964, 3.0
1700493105, 64965, 3.1
1700493110, 64966, 3.2
1700493115, 64967, 3.2
1700493120, 64968, 3.3
1700493125, 64969, 3.4
1700493130, 64970, 3.5
1700493135, 64971, 3.6
1700493140, 64972, 3.7
1700493145, null, null