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Windows 10 File Explorer Transfer Speed issue

I move a lot of files from one place to another and with a specific combo of 2 of my storage devices I noticed a strange behavior:
When moving Data from one SSD to another SSD Transfer speeds are usually 300-400MB/s (Max: 500MB/s).

but when moving data from one SSD to an HDD, the data Transferring speeds fluctuate randomly. Ive noticed that in regular intervals, the speed which is shown in the File Explorer goes up to 1GB/s, doubled the claimed maximum speed of the SSD, and way higher then the claimed 100MB/s of the HDD. I’ve looked into it and the average speed is always ~90MB/s. Is this some kind of error in the file Explorer, or has it something to do with the storage devices itself? How to fix it?

Info:

OS: Windows 10 Home

Encryption Software: Truecrypt 7.1a (Do NOT comment that it has security issues)

Storage Device referred to as “HDD”: https://www.amazon.de/dp/B0713WPGLL

Storage Device referred to as “SSD”: https://www.amazon.de/dp/B07QND4VZ6

CPU: Intel i7, 4 cores 2.5GHz

RAM: 32GB DDR3, 1333MHz

GPU: GTX 980M (20GB Version)

Data beeing transfered:
.rm
.mov
.mp4
.avi
.AVCHD
.WMV
(all in video form)

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