Using dolphin, file is copied OK but after removing external HDD there's just 8MB of it

I am copying a 817 MB video file to an external ext4 USB HDD with Dolphin on Endeavour OS with i3wm. Kernel 5.10.32-1-lts
File copies ok. I open file inside external USB HDD and I can play it ok. Full 817 MB are on it.
I safely remove drive with dolphin UI. Then I connect USB HDD to computer again (or other computer, it’s the same), and There’s only 8MB of the file (8.388.608) (and once it was even a 0 byte file)
There’s still 3,2 GB free on external HDD.
I have done this many times but haven’t been able to copy the whole file.
If I copy using terminal, with sudo cp, everything works ok.
Is this a dolphin bug?

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