Pi freezes when transferring files over network (WiFi)

[Sage Freke]

Hi, I use a samba share to transfer files over WiFi.
Everything works as intended except that after a few hundred of files windows explorer reports a connectivity error and the pi freezes. At that point the only thing I can do is a hard reset to reboot.
What could be the problem here? I know for sure that it's not a screensaver issue: not only I turned it off, but without file transfers I can leave the Pi sitting in the menu for hours. And this seems to happen only when transferring files over samba: I left it cover-scraping the entire SNES library and it didn't froze (it took a while, maybe an hour or two).

EDIT: I tried to transfer files trough sftp with filezilla and guess what? the pi freezes.

EDIT2: I tried a transfer over SMB while in command line mode (F4): when the pi inevitably froze, I got a lot of gibberish on the screen which ended up with "Kernel Panic - not syncyng : Fatal exception in interrupt"

My raspberry pi is a model 1 B+ with the following USB devices attached:
a WiFi USB adapter (I don't remember the manufacturer, but I bought specifically for the Pie)
an iBuffalo SNES-style USB controller
a mini wireless keyboard with trackball

My power source is a Vultech 2A charger (I've never seen any rainbow on the upper right side of the screen).

Retropie version 4.2
Emulation station V2.1.5RP
Built From: pre made SD Image on RetroPie website transferred with Win32 Disk Imager