QImage Ultimate 2022-120.
Windows 11.

I just made some editing to a bunch of TIFF files with GIMP 2.10.30 and none of them are recognize as valid files by QImage.
Looking for a solution I have found this on a recent GIMP version changes:

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TIFF exporting used to lock the TIFF files because of a bug in the Windows thumbnailer (Explorer.exe would acquire a lock on the file and never release it). Since Microsoft doesn’t seem to want to fix this long-standing bug, we decided to switch to another way of creating thumbnails by adding a “reduced-resolution image” as the second page of the TIFF, as proposed in the TIFF specification, instead of adding a subifd thumbnail. This takes care of the lock issue in a nice way, bypassing Explorer‘s bug. Of course, it means that programs that can’t reads tags properly might try opening thumbnails as additional pages, even though it is explicitly annotated as “reduced-resolution image“. If you ever run into this very issue, please report it to developers of such programs. What they need to check is the SubFile type of the pages their software opens (as per TIFF specification).
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I hope this can help solving the issue.
Mike, if you need a sample problematic TIFF, please, ask.
Thank you for your support.

Here you have:

https://mega.nz/file/GG5j3DBS#z4Dyl0C7JBuHGngzO7ei3hGpp6URevBCUIw2NWux04M