horizontal colored lines appearing after saving a PSD in PS

UPDATE: after a month of working on hundreds of images without problems (so far), I can probably say that the issue depended on the fact that my external drive was formatted with ExFAT.

I decided to switch the hard drive to MacOS Journaled format, and had no problem since.
Moreover, when I used the previous hard disk, which is still in ExFAT format, I got some other "horizontal lines" issues..

Yesterday, I also stumbled upon this article, which talks about problems with Sonoma and ExFAT formatted hard drives: https://forums.appleinsider.com/discussion/235967/external-drive-support-in-macos-sonoma-is-partially-broken-and-its-probably-apples-faul   

"Hello! It sounds like you're experiencing a frustrating issue with horizontal colored lines appearing in your photos after saving in Photoshop. This could be related to several factors, including graphics card drivers, cache settings, or even a specific bug in the software. Since this is a new problem with your Mac Mini 2 setup, I recommend checking for any updates for your graphics drivers and ensuring that your Photoshop and Lightroom Classic are up to date. Additionally, try clearing the cache in both applications and see if the problem persists. If the issue continues, consider reaching out to Adobe Support for more in-depth troubleshooting. Good luck, and I hope this gets resolved soon!"

Feel free to adjust the response to better fit your situation or let me know if there's anything else I can assist with

today's update: yesterday i threw the "corrupted" file in the bin. Today I looked for it in the bin, and magically the purple line is gone.

https://helpx.adobe.com/vn_vi/photoshop/kb/networks-removable-media-photoshop.html 

I know, but it happens on different ports, and different harddisks

The issue could be related to the physical port itself on the computer.

That would be a very huge limitation, and at this point very unlikely depending on hardware problems (which was your point). 

Adobe helpdesk, which I also contacted, hasn't talked about any problems in using external drives (which is something that almost every photographer I know does constantly), neither suggested to only use the internal drive, but is still trying to figure out what could be the reason.. 

I think that proves my point very conclusively. Save to local drive, then copy over. Don't save directly to an external drive.

I did so. I worked on the local HD, and no corruption happened, so I thought it was a problem with the external hard drive I was using...

BUT, yesterday I bought a new external drive (with its own new cable), formatted it, connected it to a never used before port and started using it, and today I got the first corrupted file already. The chances of this being a hardware problem seem quite low at this point..

This is very easy to find out.

Work on the local drive for a while, a month or so. If you get any corruption during that time, come back and I'll reconsider.

Something in your hardware is corrupting your files. So you have a choice. You can either take some precautions, or you can take your chances.