wifi sync not working/ unable to identify each other device via wifi

[Shower Chan]

Hi,

I recently bought Galaxy S3 as my first Android phone. Then I first start to care about WiFi sync as it's so convenience.

Please help me as I've tried all attempt and unable to identify what's the problem

- I used iSyncr & WiFi File transfer Pro to transfer file
- I start above sync App in Galaxy S3, device can be identified and Sync work just fine
- After a while, or could be days, or maybe after a huge file sync, I no longer found my Galaxy S3 via WiFi from other device. it just won't show up
- turn Wifi Off/on, restart Galaxy, restart PC won't help
- Internet connection still valid, only device cannot found each other
- I've configure windows firewall and open a port for them
- Turn router Off/On then everything works back fine

- I have 2 Win 7 PC, 1 Win XP computer all connect to the same network with my Android phone
- when everything works fine, I ping my phone and got all responses
- router is DSL-2640

I searched multiple forum and some said uPnP, I check uPnP is Enabled/On in my router setting.

I suspect this is a router issue but strange that I couldn't found any setting regarding this.
So frustrating because if I turn router off then on, everything just fine.


Any idea how to fix?