This has been normal for me ever since ... well ... a very long time, across different file managers, eg. Explorer, DOpus, etc.
Normally I'd have to do a Properties on the relevant file and then refresh the display to get the current size.
Oddly enough it seems to be random sometimes, eg. writing an MP4 video file will:
- sometimes show a steady increase,
- sometimes just sit at 0 until it's closed,
- or sometimes show a steady increase but only after forcing the system to interrogate the file, (eg. Properties).
A F5 refresh alone doesn't seem to initiate a return to increasing file size.
Maybe it depends on the way the file is being written and/or the filesystem of the destination?
eg. One long continuously open write as opposed to the file being closed between successive appends.
I just ignore it now until I see the process is finished.