Why does the HDD periodically fall off in a computer that still has an SSD?

Question

Hard disks

Hello
, SSD is not even a year old, HDD (1tb) is also not very old - 1.5 years. Computer 8 years old (assembly on socket am3, PSU 400w, video card)
There is such a problem: a year ago, an SSD was installed in addition to the existing HDD, and the HDD periodically falls off all this year (everything worked fine before the SSD, except for the fact that the previous HDD broke for an unknown reason, but it was already old, so it was bought new HDD). For example, during operation, the HDD disappears, and since the axis and programs are installed on the SSD, everything continues to function. And if after this you simply restart the PC in order to try to initialize the HDD again, then in general everything can get up at the boot stage (although the main boot device is set to SSD, which works fine separately from the HDD). After a certain number of reboots (with different time intervals), the operating system still loads.
But that's okay. If you turn off the SSD, reinstall the system on the HDD (that is, do everything as it was before the SSD), then the HDD works and does not crash. Could it be the power supply? I don't think so. I personally have another vivid example of another computer with a smaller PSU (350w) and more powerful consumers - a video card, a cooler, and most importantly, SSD and HDD are also together - there are no problems with lack of power. Plus, as you know, HDD and SSD consume 1-5 watts in total.
So, back to the first computer. In general, sometimes these HDD/SSDs work in pairs normally for whole weeks, I even tested the stress tests with aida64 for several tens of minutes with all the checkboxes checked - there were no failures. Crashes occur at random times and the cause of the crashes, as well as the subsequent problems with loading the OS, are unknown.
What has been tried so far: switching sata cables in different ways, as well as replacing them with new ones. Reinstalling the OS (Windows 8, 10, Linux), now it's windows on the HDD, linux on the SSD, but it didn't help (almost) - the same problem as in the text above, if they are connected together - crashes happen even in Linux, and this despite the fact that it is on an SSD, but separately, by disconnecting one disk, the system (windows or linux) works fine on the second one, which means the problem is not in the SSD, HDD and cables).

Answer 1

Try all the same, just in case, to make a diagnosis of the hard drive using the R. tester , what if this will give additional information for reflection?
If not, then I would also try to replace the PSU, and also delve into the BIOS settings.