Connection abort using WiFi

Good evening, it's my first time here!
I'm an happy WinSCP user. :D

I use it to connect to my Kindle Touch using USB cable or WiFi connection.
USB connection works really fine, but I have a problem with WiFi connection.
Every time I try transfering a file to/from Kindle, I get the "software caused connection abort", my WiFi connection drops and I end with a broken file which leaves a .fuse_hidden.
This happened with file above 100-200kB with WinSCP version 4.0.3.
I upgraded today to last version (5.1.1) and now I can't even transfer an empty txt over WiFi (connection is aborted as soon as I click on transfer).

I have the same problem when connecting to my Android phone over WiFi, so this is not device-dependent.

Here are some info:
- windows xp
- WinSCP version: 4.0.3 and 5.1.1
- SCP protocol over WiFi
- I'm using the GUI

Thanks to everyone!!!

Try disabling Optimize connection buffer size
https://winscp.net/eng/docs/ui_login_connection

Please, let us know!

No luck! :(
I also tried changing every keepalive option (it was my first thought)!
Every time I try to transfer something, the connection drops and my router reboot!
I can provide my WinSCP.ini config file if needed!
Thanks again!!

This could be helpful:
if I lower the transfer rate, it waits longer before ending in connection abort (and connection drop + rounter reboot). This means more KiB!

Here are some results:
64 KiB/s ==> 156 kiB
32 KiB/s ==> 204 kiB
8 KiB/s ==> 260 kiB

Any news? :oops: