Update: The project I sent to the mechanics have at least 10-6 sprites having this bug.
“Lu - costume11, costume7, costume8, costume24.” “Vase - costume5” “Null - costume1 (36)4, costume16” “Vivi2 - costume2.” “Vivi4 - costume40” I went on to my chromebook and the others were targetted and the same sprites mentioned here are still targetted.

Update once again. I contacted the ST about this. Hopefully they will fix it soon

it might be because of the scratch port issues??

I have this issue too, I hope its a reversible error, but this is certainly a terrifying predicament. I always make backups of my projects in case something like this would happen, but this is greatly upsetting as a long time scratcher.

Question: What happens if there are question marks in your unshared project? ( to be specific )

Can't replicate, even with projects that have a lot of assets:
My browser / operating system: Windows NT 10.0, Chrome 148.0.0.0, No Flash version detected

Hello,
I will leave this message as I just became one of the people who are being affected by this issue this morning, and I had heard that the team needs some sample to work on to fix this issue.

In fact, I haven't experienced this issue until this morning, and this project, (https://scratch.mit.edu/projects/793162782/editor) (Just in case:My browser, operating system: Windows 11 25H2, Brave 1.90.124 (Chromium: 148.0.7778.179)) is the first one to be affected so far. (I have taken my first backup just now, after the issue had occured, so I think I would be off safe with my data, if any further damage was caused.)
As other people have been saying, this project is indeed an unshared project, and no other shared, or unshared project from me is currently being affected.

Random costumes of random sprites seemed to be affected, so I would also suspect that there must have been some kind of curruption in the server's data, indeed.
Example of such sprite in my project were (key: sprite - costume): 誕生日カード - コスチューム1 / スプライト1スプライト1 - コスチューム2, コスチューム4, コスチューム6, コスチューム12, コスチューム13, コスチューム9 / スプライト8.- コスチューム1 / スプライト13 - コスチューム1, コスチューム2, etc.(perhaps this is happening because the sprites' and costumes' names include foreign characters, not just the regular alphabets and numbers…? probably not.)
When they turn into such question-marks, that specific costume just gets entirely replaced with the costume of the gray square box with a question-mark in an editable text box, for the .svg's. For the .png's the costume just seemes to be the baked version of the raw question-mark sprite. When you try to look into the costume in the costume tab, the question-mark would be displayed with an offset.

Hopefully I was lucky enough to have this issue not affect the important bit of my data, so I havn't gained any emotional damage that other people may had to have to go through (yet). To me, it doesn't have to be urgent, but would I hope that this issue will isntead be patched surely.

Thank you for your time, and I hope we will be successful in getting over this issue!
Have a nice day.

So this issue has been happening mostly on my unshared projects
so i wont be able to share a bunch of these, but it has also happened on other projects.
https://scratch.mit.edu/projects/1191511669/ (this one's currently fine, but some of ‘'2011’''s costumes were those weird question mark things.
The rest of the problems i have found are in unshared projects.

https://scratch.mit.edu/projects/1260355275/ I just checked out my miss you project and omg…

https://scratch.mit.edu/projects/866887651/ My project's also been affected, too. I also think the audio/music could have been corrupted along with the sprites.

At some point, a few of my projects also got hit. Two of them (those being timelines) have been restored (due to me working overtime to fix them), but one is still completly messed up with the grey ? squares. Many of the audio I used has also glitched (from what I mean, the audio is completly blank).

nope nvm it's still not wroking

Oookay, I just reported it to be stickied. Btw, hi Twelvie!!!

My browser / operating system: Windows NT 10.0, Firefox 151.0, Flash 32.0 (release 0)
Yeah, one of my unshared projects has this issue. Do you think the kumquats got tired of eating signatures, and started eating sprite costumes?

I think they're starting to evade shared projects too, since I looked at my Psybox slatch take mods, and guess what, they got all question marks, including the background, that I had to announce it in my own diehardc server.

It's fixed for me now!

Some of the projects I own still have the question marks, and have the 0.00 bug. I'll keep this topic open / my time tracker shared until further notice. :<

My entire game is unplayable because of the grey question marks. The ground hitboxes are also not working. Some of the music is gone. I didn't do anything! I left it for five days, then when I opened it again, everything is broken!!! https://scratch.mit.edu/projects/1138818431/

Some of the music says 0.00 and is completely gone.

Yay some of the sprites got fixed
but now there are other sprites that are gray question mark boxes

please fix this