Speed syncing to external USB HDD became worse

[wroot]

I have tested FreeFileSync with that external drive before starting to use this tool and at that time speeds were acceptable. It was maybe 4-5 versions before. But for the last 4 months i have noticed that sync is struggling with big files. If i try to copy same file manually in File Explorer it maintains 20+ MB/s and copy takes a few seconds for 150 MB file, but in the tool it starts with 20, but quickly goes below 1 and stays like that for the most of the time, so my sync time increases a lot. Tried changing threads numbers, but it doesn't have much impact. I wonder what else i can do or check. The drive is the same and OS is the same (minus the usual monthly updates). I sync same files between two internal HDDs and it is fine.

[wroot]

Just as i have posted this i tried to sync same files again (some already synced in a few previous tries, so not exact same set) and it maintained 40-50 MBs in 2 threads. It is like it doesn't like some particular files or something and takes ages to copy them.