Hi Philip,
Thanks for posting in the community, I’ve tested on my side, it worked well when I tested using File Explorer and browser.
Please try to replace the file by going to SharePoint online site, you can drag the new file into the document library and replace the old file.
In addition, to narrow down the case, please provide the following information:
1.
Does the problem occur on ONE specific file/folder or ALL SharePoint files/folders?
2.
Will your other colleagues have the same problem?
3.
Will the problem occur on locally files?
Please feel free to give me feedback if there is any progress and I’ll continue to help you.
Best Regards,
Arck