We have a fairly “stock” up-to-date version of WordPress. Our theme is custom, but doesn’t involve any of that sort of low-level functionality, and hasn’t been substantially modified in a long time. We are on IIS, but have been all along and it used to work just fine. Our PHP is 5.4, which I didn’t realize until just now. That seems insanely old, but WP itself doesn’t seem to mind. I guess I should upgrade it whether it helps this problem or not.
At 807 bytes, it’s not even the database. It is a dump file, but it only contains the create statement for the first table, wp_commentmeta. Not even any inserts, just the create. I did a mysqldump last week to make some clones to work on, and that always completes in under a minute.
I just did a manual files-only backup; it ran for a few minutes and then acted like it was done but didn’t create any files in the backup directory, nor entries in the UI. The process does create a temp file while running, but that file disappears long before the plugin claims to have completed.
