My assumption is that the PC is busy doing something else and the very simple board used in printers have no buffer to speak of. This was a problem for me using window 10 and a dedicated E6040 Laptop with 16 gig of ram and an SSD driver. Running from SD card was flawless.
I finally spent $90 on a Raspberry Pi 3B+, power supply (Cannakit) and a Logictech C270 webcam.
I used an extra monitor, hdmi> vga converter I had, USB mouse and keyboard and a case I printed off Thingivers. This works flawlessly, I have remote connectivity and view from any device as well as locally next to the printer. The process is slice with S3D, save to tool path (save local on pc, or nas, in octoprint, upload,load, and print.. No stopping no swapping sd card.
I've had that issue. To fix it all I had to do was reboot the PC. I think part of the problem for me was I tend to put my PC (Win7) to sleep at night instead of shutting it down. Windows wake up is always a roll of the dice. A lot of new oem PCs especially with windows 10 go to sleep or hibernation when you "shutdown".
If all else fails I would shutdown the PC and printer. Then pull ALL cables and let it completely dissipate for a minute or two. I've seen a PC lose USB capability, just unplugging power cable didnt fix. Since the video, ethernet, and self powered usb devices have a carrier signal line, it was enough ambient energy to keep the motherboard from completely dissipating. Also disconnect powered hub if your using one in the mix. I've had those cause intermittent Power Surge on Hub events even though they were self powered. You could also adjust Advanced Power settings and try disabling USB selective suspend setting to remove it as a possible corner case problem. Last but not least, if your using an inherently flaky USB 3.0 port, try a USB 2.0 port instead.
EDIT: Now that I think about it, just to be thorough, when I had USB pausing I also had a strange video issue. PC im using has an Nvidia Quadro NVS 290. Dual monitors that I routinely have netflix playing on one while I'm tinkering. Rarely when I would wake the PC up, screens came up fine, but Netflix would not play any video. Launch a diff browser, same problem. No errors, just hit play and nothing while the timeline scrollbar shows that it is. Really odd. Its possible that its the nvidia driver is causing a kernel race or contention, in turn causing other system drivers to pause.
Does your printer include an SD card slot? If so, have you tried running prints from the SD card rather than over USB?
What OS are you printing from? OS X has app nap and more recent versions even have other features which are difficult to disable without installing software with that in mind. Windows has the ability to put specific USB ports to sleep and sometimes will even default to that behavior if you're not plugged into AC (laptops only).
Essentially there are a lot of factors in play, most of which have been mentioned already on this forum. I'd try SD card first if that's an option, as USB serial communication is known to be less reliable than reading from an SD card.