I've been a linux system admin for a very long time (started as an ISP support tech in 1999).
I lost some time and prints to this issue after replacing the hotend on my creality ender 3 v2 neo. A cable that had worked flawlessly for dozens of prints now seemed to be ruining every single print attempt. I was having the issue where it would put down 1, 2, maybe a dozen layers fine and when I would come back later to check, it would be printing in mid air like another post I found about this. I did a lot of troubleshooting to ensure it wasn't some other variable causing it, and the exact same file would print flawlessly when done from the sdcard.
The advice in this forum for this kind of problem is to try another USB cable.
I don't know if that is good advice or not, but the main issue I have with this is; How can I tell if a cable is good or bad? Is there a device I can use to measure it? If not, this advice doesn't really help me if my goal is to print without hassle.
The truth (for me at least) is that if it is possible that I could use a known good cable and it can just go bad at any time causing my prints to fail, then this isn't the solution for me.
I thought I saw somewhere an adapter that goes into the sdcard slot itself, not the microusb, does anyone know about those, and are they more reliable?
I'm using a libre (le potato) running whatever their image is for it.
This is not how communication issues caused by the cable tend to show themselves. If the printer has stopped extruding, but is still moving, then there is something else that has gone wrong. If it's still moving, then the communication is still working OK. Normally, you would experience either resend issues (which would mean printing temporarily pauses while communication is retried) or it disconnects completely from OctoPrint. So my first bet is that you don't have the same issue as this post is talking about.
If we assume you do have communication issues:
It does happen that cables get damaged or stop working as well, but this is really rare compared to the number of times people start with a bad cable first, so the general advice of fixing communication issues with good cables is definitely valid & there's a lot of success stories of just buying a new cable. It's quite hard to measure and rate 'how good a USB cable is', but if you want a good one, it would have the following qualities:
Short as possible
Shielded
Ferrite cores can help
Higher quality - this is subjective, but what I mean is not some flimsy thin cable, one that is actually properly made.
That would be a completely different system, you can't communicate with the printer like that. It would replace the step of swapping SD cards manually, but all the control of the printer would be done directly at the printer itself. Just literally the process of uploading to the SD card is replaced there.