When uploading a new version of an existing file here, the dimensions are shown as "0 × 0 (261 KB)". This is the correct file size in KB, but the dimensions should be 1771x685 px. While the image is displayed correctly here, it does not display correctly on the Wikipedia pages that use it, and the thumbnail at the top of the File page is also broken (just a blank rectangle).
I tried to correct the problem by saving the file in a different program and uploading again, but the error persisted. I have also tried to undo my edit, but it wouldn't let me do, saying my edit had already been undone (this does not seem to be the case). I then asked for help at the Help desk, and a different user (Jeff G.) has since tried to undo it. Their attempt to get the file back to the old version were unsuccessful, the dimensions are still broken, "0 × 0 (108 KB)". 108 KB is the correct size for the previous file version, but the dimensions remain at 0x0.
My browser: Firefox 89.0.2 (64 bit), on OS Windows 10. File created with MSPaint (1st attempt), then with GIMP2 (2nd attempt), same result with both. User Jeff G.'s failed attempt to undo the edit suggests they were able to reproduce the problem. I have not attempted to reproduce the problem with another file (upload a new version for another image), to avoid disruption.