The issue is in fact affecting many more feeds than I had realized.
I am sending index information from my electronic utility meter at a 10s interval, and unavoidably about 10% of the values are missing.
When I graph that feed with the “delta” option checked I get those CSV values:
timestamp, index, irrelevant
1562490170, 2.0, null
1562490180, 1.0, null
1562490190, null, null
1562490200, 11648190.0, null
1562490210, 2.0, null
1562490220, 1.0, null
1562490230, 1.0, null
1562490240, 1.0, null
1562490250, 2.0, null
1562490260, null, null
1562490270, null, null
1562490280, 11648199.0, null
1562490290, 2.0, null
1562490300, 1.0, null
1562490310, 1.0, null
1562490320, 1.0, null
1562490330, 1.0, null
1562490340, null, null
1562490350, 11648207.0, null
1562490360, 1.0, null
1562490370, 1.0, null
1562490380, null, null
1562490390, 11648212.0, null
1562490400, 1.0, null
I will explore the input processors to see if there is a way to log the last input value to a feed when the input goes missing… but if input processing is triggered by the input being updated I assume this won’t be possible?