Everything keeps roting to hell without any apparent reason. Crop rotation is reasonable and all related parameters (fertility, rocks, etc) are more than perfect! There are enough villagers, enough storage for all produced crops to be stored! Yet this keeps happening again and again, save after save leading to the death of the village!
how many beee heeves do you have
While you say you have enough villagers are enough of them farmers?
And you say it happens again and again, yet you haven’t made a bug report about it with the saves it happens on linked so the devs can have a look at it.
The topology is as follows…
12 fields each 12x12 with 7 workers equals a workforce of 84 villagers. There is never a shortage of farmers whatsoever.
Number of grain storages: 7 x 1800 = 12600 of total storage capacity exclusively for grain. These are located next to fields and centered for faster access and less travel time. Also rat catchers everywhere.
Total (potential) grain output for 3 fields is somewhere around ~ 2600/3400 each which equals no more than 10200.
Fields output the same crop but have a distance amongst them in order to minimize disease spreading.
I have 12 millers working around the clock + 2 breweries so storage is no problem. These are also located strategically for faster access time. Notice: I don’t allow high accumulation of grain.
A lot, a f ton of them akshually…but those are managed by spare villagers which are more than 100.
I would produce more grain, lots more and produce bread and beer and cut down on Flax. More cattle I’m running 5 with 650 pop. Start preserving and at least 6 smokers, but more like 10. Definitely increase wheat production by x20 at least. You can get by with less farms, I never need more than 8 at 8x9 when I play. Why 8x9? they only take 3 farmers any bigger and its 4.
Can’t tell from the screenshot, are any sides of your crop fields touching another crop field?
Or, do they all have at least one space between them?
Do you conserve the food? That helps to prolong the the life span of the food before it rots.
12 millers sounds a lot. I think I have never used more than four. As I recall, grain is actually less prone to rotting than flour. So storing the grain as grain will make it last longer than quickly refining it to flour.
This happens on prolonged 3x speedplay only. Once I switched back to x1 speed things came back to normal.
The problem is bundled with the 3x speed. I had some speculation over this but after extensive gameplay i come to the conclusion that most bugs in the current state of the game have to do with 3x speedplay and the low frame rates. These two are tied somehow together. As such 3x gameplay has definitely to be addressed.
Weird. I always play at x3 speed and haven’t had this happen. Admittedly I haven’t run a town up to 140 years and 800+ people, but do get up into 30s and 40s with 300-400+ people and not seen this. Maybe it’s something to do with the number of years a town is going for combined with the higher population. 
Try this save of mine. These screenshots come from this particular save. Try on 3x. Also be advised that I am currently waiting to upgrade GPU since the one I have now is a decade old card. I think once I have enough VRAM things should work out.
Looks like rounding/truncation/precision issues. I tested it out up to 50X speed
and it all falls apart real quick at 50X. There could be other reasons
as well.
I test all these things at 3x and 10x without issue. That is not the sole factor. As I asked in the thread you linked, I’d be curious to hear your system specs.
I’m, uhh…not too worried about 50x.
Yeah 50x was just a test to see if I could make it fall apart quickly so I could be
sure something was going on vs 1x. I never see these issues at 1x.
Yeah I would never play at that speed! 5x would be where i would play
(3x is just a tad slow for me) The thing is if it goes wacky I quit the app
load in the game and it is almost always fixed. I can tell it is happening
when my food (one example) for no reason disappears and nothing has changed.
I go from like 14/1 to 1/0 in 1 year. I reload and it is back to 14/1
Note that is the extreme case most of the time it is a gradual downward spiral
over say 5 years. I now restart the game every 2 hours to keep it stable/reset
else strange stuff happens (as well as FPS drops)