Simple setup: Inserter inserting barrels of water in an unbarreling machine.
At least once every 12 hours of playtime the inserter just stops inserting

Thank you for the bug report 🙂

May you provide the exhaustive list of all mods you use?
And can you provide more details about the apparent state of the machine? Like when hovering, it should be able to tell you what is wrong (something like "destination full" or similar)
And finally, are you sure there is never a single barrel that is not water going into the machine? Because nothing prevents different fluids to be outputted consecutively.

I just ran a little test just to be sure, passed 3 million recipes completed without issue (that's 25 hours of playtime).
Internally my machines are just simple furnaces, there is no script or any complicated shenanigans.
Other mods are most likely involved but I will still try to pinpoint the issue.

Thank you, I will attach a mod list below. I agree it seems to not be an issue with this mod, however I don't experience this behavior with any other machines.

The machine states "No ingredients". The inserter states "waiting for source items". The chest it is pulling from is completely full of water barrels and the way the cest is filled is filtered.

"base",
"aai-containers",
"aai-industry",
"aai-signal-transmission",
"aai-vehicles-ironclad",
"Actual_Craft_Time",
"AdditionalPasteSettings",
"advanced-centrifuge",
"AdvancedArtilleryRemotesContinued",
"alien-biomes",
"auto-barrel",
"AutoDeconstruct",
"automatic-station-painter-continued",
"Automatic_Train_Painter",
"AutoTrash",
"beautiful_bridge_railway",
"belt-visualizer",
"BetterAlertArrows",
"blueprint_reader",
"bobenemies",
"bobinserters",
"boblibrary",
"boblocale",
"BottleneckLite",
"bullet-trails",
"chest-auto-sort",
"combat-mechanics-overhaul",
"compaktcircuit",
"Constructron-Continued",
"CopyPasteModules",
"cybersyn",
"cybersyn-combinator",
"DragonIndustries",
"dynamic-robot-queues",
"early_construction",
"EditorExtensions",
"ElectricTrain",
"Enhanced_Map_Colors",
"equipment-gantry",
"EquipmentGridLogisticModule",
"even-distribution",
"EvenDistributionLite",
"EvoGUI",
"factoryplanner",
"FactorySearch",
"Fill4Me-fixed",
"FilterChests",
"Filter_Combinator",
"flib",
"Flow Control",
"FluidWagonColorMask",
"FNEI",
"Future-Technology-Factorio-Modpack-sek2",
"Geothermal",
"ghost-counter",
"GhostOnWater",
"GhostScanner",
"GhostScanner2",
"GhostWarnings",
"glutenfree-se-rocket-launch-pad-label",
"grappling-gun",
"GUI_Unifyer",
"HelfimaLib",
"helmod",
"informatron",
"inserter-throughput",
"InserterFuelLeech",
"inventory-repair",
"jetpack",
"Krastorio2",
"Krastorio2Assets",
"LogisticRequestManager",
"LogisticTrainNetwork",
"LtnManager",
"map-tag-generator",
"Milestones",
"mining-patch-planner",
"ModuleInserterEx",
"ModuleInserterSimplified",
"MouseOverConstruction",
"multi-product-recipe-details",
"nco-AdvancedAirPurification",
"Orphan Finder",
"PickerDollies",
"PipeVisualizer",
"pollution-scaling",
"power-grid-comb",
"pump",
"pushbutton",
"qol_research_jatmn",
"QuickItemSearch",
"RateCalculator",
"Reactor_Interface_Tweaked",
"RealisticDecorationCleanup",
"rec-blue-plus",
"RecipeBook",
"Repair_Turrets",
"ResourcesScanner",
"robot_attrition",
"rocket-log",
"rusty-locale",
"SantasNixieTubeDisplay",
"scootys-armor-swap",
"se-core-miner-output-helper",
"se-flow-control-bridge",
"se-recycling-extras",
"shield-projector",
"show-max-underground-distance",
"simhelper",
"simple_landfill_mining",
"solar-calc",
"some-autoresearch",
"space-exploration",
"space-exploration-graphics",
"space-exploration-graphics-2",
"space-exploration-graphics-3",
"space-exploration-graphics-4",
"space-exploration-graphics-5",
"space-exploration-menu-simulations",
"space-exploration-postprocess",
"space-spidertron",
"Squeak Through",
"stack-combinator",
"stack-size-tooltip",
"stack4cc",
"stdlib",
"StorageTank2",
"Tapeline",
"TaskList",
"textplates",
"Todo-List",
"train-log",
"train-scaling",
"train-upgrader",
"TrainGroups",
"VehicleSnap",
"water-consumes-pollution",
"wret-map-colors-fix",

That's way more mods than I expected for sure 😅
I think I know what the state is, the barrel item is most likely not recognized as a valid item in the unbarrelling machine.
To check that, can you confirm me that manually putting a water barrel in such "bricked" machine is also not working?

And in case the item is indeed not allowed, may you check another kind of barrel just to be sure all of them are affected?

The odd thing is that if I simply rotate the inserter and then rotate it back it works as normal. Inserting manually works as well.

The issue only occurs every now and then where the inserter simply stops inserting barrels which I only notice because the production eventually grinds to a halt.

I have now set up a line of 8 huge buffers connected to 8 unbarreling machines. Each line has its own type of fluid and every one has stopped at some point. (But not all of them at the same time). Since the issue is so rare and I have so many mods I don't have time to isolate it to a minimal reproducible state.
I am happy to share my save file if that helps.