On iPad, this has been happening for quite a while, on both stable and beta versions, and before the last few iPadOS updates.
There is a white flash on the screen most always. 80-90% of the time, but not every time. This happens after hitting “save to files”.
This slow motion video shows the problem.
Limited testing, but this seems to be gone in 5.490!
Update: Even though this bug seems squashed when exporting in my “normal” fashion, I can force the visual flash. To create this, before “save to file” click the “share” function. It is no surprise that share is not working, but then, save to files and the flash is back.
These are coming from the OS, we are just calling them when you press the button. So unfortunately whatever happens after the button is pressed, is up to iPadOS, including how it animates / populates these modals.
Thanks, @Laci_K !
There is a difference with the 5.490 beta though. The “flash” is much improved when one does not first hit the share button. In 5.473, the flash was very frequent (guess 80% of use) without ever touching the share button. (I knew that button would not work so I avoided touching it) Now it is much better, I didn’t see it in about twenty .3mf exports. And if I hit the share button first, the flash bug is back reproducibly.
Is Shapr3d working with Apple to fix the share bug? Seems like you should have “an in” with Apple after winning their design award! 
If the Share button is “poison,” and you know it doesn’t work, why don’t you remove it as an option until Apple fixes it? How is it that a program like Concepts is able to share without a problem? Do they know how to work around the bug?
All of what I am describing is with the same version of iPadOS 17.0.3 (21A360), so Shapr3d has done something to work around the Apple bug in some fashion.
It is obvious that the Shapr3D teams have worked very hard, and the 5.490 release has fixed many bugs and it shows! I also know that you have a lot of great things coming, like folders (yay!) and other important stuff. Thank you! 
Keep up the great work. 
Is Shapr3d working with Apple to fix the share bug?
Unfortunately no 
We did report the issue to them multiple times though.
We also don’t know exactly why it doesn’t work. It doesn’t work sometimes for some users, and it has been around since iOS 13. Removing this indefinitely would mean taking it away from the majority of the users who actually have no problems.
I can guarantee you we changed absolutely nothing in this area, in years. We call the OS modal with this button, and that is it, at that point it’s out of our hands.
It also breaks in other apps, and don’t break for every app at the same time.
Thank you, Laci.
I didn’t mean to suggest that you had done something with the modal share button. Rather, pushing it not only does not work (just a blank panel for me) but that after pushing the share button that the flash problem comes back on the save to file button. And that not pushing the share button, the save to file button seems to be fixed with regard to the flash problem.
Just pushing the share button has consequences beyond the share functionality.
It sure seems to me that something changed in 5.490 that helped reduce (eliminate?) the flash bug when hitting the save to file button.
I do not see the flash any more with the 5.490 update! (as long as the share button has not been touched.)
Great job, and thanks, Shapr3d teams!
EDIT: Sorry, I posted “solved” too soon. After using Shapr3d for hours, the problem is there. Even without touching the share button.
As far as I can tell, this bug is gone! Thank you!