Last week, I did an in-place upgrade of my SharePoint 2010 Foundation server, from Server 2012 R2 to Server 2019. Ever since then, I am unable to open files of any type that are over a certain size. I have narrowed the size to between 5097 KB (works) and 5192 KB (doesn't work). This affects PDF and PPTX, and probably other large file types as well.
The "404 NOT FOUND" error happens when opening files through the browser. When opening files through Webdav, I get a different error message, such as "Adobe Acrobat could not open 'FILENAME' because it is either not a supported file type or because the file has been damaged." for a PDF.
My gut instinct is that a setting was changed in SharePoint or IIS during the upgrade. I've been searching Google for solution for about a week, and the most common suggestion is to check and increase the various file size limits.
In web.config, I have set maxAllowedContentLength=2147483647.
In applicationHost.config, I have set maxAllowedContentLength=1073741824 (I left it as it was).
In the ISS logs, I see this series of events (removed the filename as it is confidential) when I try to open a file:
Entering monitored scope (Request (GET:FILENAME)) Name=Request (GET:FILENAME) 3106c6c5-4199-41c3-a7bc-0af45331e2c8 af71 Medium HTTP Request method: GET 3106c6c5-4199-41c3-a7bc-0af45331e2c8 Overridden HTTP request method: GET 3106c6c5-4199-41c3-a7bc-0af45331e2c8 HTTP request URL: FILENAME URL 3106c6c5-4199-41c3-a7bc-0af45331e2c8 Leaving Monitored Scope (Request (GET:FILENAME)). Execution Time=5.9737 3106c6c5-4199-41c3-a7bc-0af45331e2c8
Is there anything else I can try? Some of the documents that are inaccessible are quite important.