The bug
If you drop multiple stacks using ctrl+q some of them might disappear. Example: grab 27 stacks and hold ctrl+q and move your mouse over your inventory you will only get 14-19 stacks back when you pick them up again, they simply disappear.
Have tested this both in single-player and multi-player (vanilla server) and I always come up short, not depending on gamemode, the stacks just disappear on me.
This also happens if you have several droppers spitting out items.
The game simply can't keep up with the items thus deletes them it seems.
Linked issues
relates to
Attachments
Comments

added a crash report, i think this might be related to the bug where if you ctrl+q items out of your inventory some of them disappears.(MC-116618) seams very similar as about the same amount of blocks/stacks vanish. if any mods/devs wants to check this one out i can boot up a server, just let me know, and provide playername so i can whitelist.

Are you hosting the server yourself, or are you using a server host? If server host, what host are you using?
Hosting it myself. Vanilla server, so no mods. The bug is present in both singleplayer and multi-player.
We do not have enough information to find the cause of this issue.
Please attach the affected (zipped) world file. If the file size is too large, please upload it somewhere else and then link to it here.
This issue has been temporarily closed as Awaiting Response. Once the requested information has been delivered, the report will be reopened automatically.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – ✍️ Feedback and Suggestions – 📖 Game Wiki
Well not sure what that will help, because the bug is in all the worlds i create so it is a game bug not a world specific bug, but here is the server world that i use: https://drive.google.com/file/d/1tY1Mk863rCvU9X2QvqJirqnGvDSPpKeQ/view?usp=sharing
The furnace array is located at -2531 19 1676 (to test it grab 27 stacks of sand or stone from the chest and drop it on the red sandstone slab by using ctrl+q (or put it in a chest/shulkerbox on top of the red sandstone slab) smelted items will come up thru the trapdoor in the floor so stand on it and wait.
i never get the 27 stacks back. running with 5 stacks at the time might get you 5 stacks back. but the more stacks you use the bigger the loss. i think it has to do with how the game handles large amount of items, it seams to freak out and simply delete some if there are to many for it to handle.
This also happens in the latest snapshot 20w22a

You showed a video on Twitter, mentioned here: https://twitter.com/pesegolsson/status/1271144468952035328
I tried repeating this in the latest pre-release in Creative and Survival. In Creative this indeed seems to be happening, but not in survival.
You also mentioned related bugs which I hope you will add to the ticket. This does not seem furnace array related.
Steps to reproduce
Open any world
Set yourself in Creative mode
Throw 27 stacks of items on the ground with Ctrl+Q
Pick up the stacks
The resulting amount is less than the thrown amount. I've tested stacks of Stone and individual swords, both had the same result. I've also testing switching to survival after throwing and before picking up. This results in less items in the inventory as well. So it seems that it's throwing related.
this also happens if you run the items thru droppers, if you "spit" out enough items at one time some of them simply disappears so its not just player related the game simply can't keep up with the amount of items and just ignores(delete) the items it can't handle. so if you have say a furnace array with 32 or more furnaces and use droppers to send the items thru a water stream to the player or a chest and you smelt 27 stacks you might in worst case scenario only get 14 stacks back.
i also did link to other bug reports in an comment but it seams to have been removed...
Can Confirm on latest pre-release
I can confirm with Thomas's steps in creative mode only. Sometimes you press CTRL-Q and the arm swings, but no new items are spawned. No items are ever deleted.

Could you please attach or link to a video showing the issue with droppers? The issue about dropping items from the Creative inventory is very likely MC-116618.
made a quick video here showing how the droppers are setup: https://youtu.be/re6LZPTaWzc in this test i ran 27 stacks of sand thru my furnace array the result of the run at 4.30 into the video.
(and no, no items getting stuck in the furnaces)
you might lose as little as a few items or as much as 9 stacks, seemingly random from time to time.
This is in 15.2. have done a few tests in rc1 and have not had any losses there yet so something seams to have changed in rc1 from pre7.

Thank you for the video. In case you are experiencing this again, could you please attach the world (zipped)?
i did add a world download in an earlier comment(02/jun), not the same as the world in the video but the same dropper setup is available in that world.

Thanks, I have tried the dropper setup at (-2532, 1677) in that world and it was broken because (without me smelting anything) there were already smelted items (stone and smooth stone) in the input slots of some of the furnaces.
After I cleared them and smelted 27 stacks, all 27 result stacks arrived.
I will therefore close this report as "Awaiting Response" for now. Please only comment if you can either not reproduce the dropper bug anymore (and want the report to be resolved as "Cannot Reproduce"), or in case you are experiencing it again. And also make sure that no command blocks or datapacks are running.
Note that the Creative item dropping is very likely indeed MC-116618.
oh sorry about the remaining items, thought i had cleared them all before i uploaded. in 1.15.2 everytime i made a furnace array using hoppers in that general layout i had losses and still do in 1.15.2!
But in the new 1.16 i don't have this problem anymore . upgraded the same world i uploaded and have tried it in a brand new world as well without issues so i guess you could mark it as resolved. unless you guys still fix things in old versions?

No, as far as I know bug fixes will not be backported to old releases.
Thanks for the confirmation, I will therefore close this report as "Cannot Reproduce", please create a new report in case you experience this problem again in 1.16.
We do not have enough information to find the cause of this issue.
Please force a crash by pressing
F3 + C
for 10 seconds while in-game and attach the crash report (minecraft/crash-reports/crash-<DATE>-client.txt) here.Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – ✍️ Feedback and Suggestions – 📖 Game Wiki