[i9505] Bad Wi-Fi?

Hello. I have a problem that I'd like help with.

I have a problem with internet connection on my SG4. Specifically only Wi-Fi.

For once, Samsung Apps/Hub says "No network connection" when I open them up and it doesn't connect, but if I turn Wi-Fi off and use 3G, it works. Same with WhatsApp, which is acting very weird. In a group chat I try to download a video someone sent, and it says "Download failed. Try again later.", but if I turn off Wi-Fi and again, use 2/3G, it starts the download of that video without any problems.

The Wi-Fi itself is not a problem I think. Other than those 2 apps and all Samsung connections, everything else works on Wi-Fi. YouTube (though sometimes it also loses connection), Twitter works excellently, DropBox, SpeedTest, Tumblr.... everything else works just fine.

It's also sometimes disconnecting/connecting randomly from my Wi-Fi connection. And it used to be a perfect connection before I tried flashing latest ROMs.

My phone's info:
ROM: Goldeneye v30
AP: I9505XXUFND7
CP: I9505XXUFNC4
CSC: I9505VFGFND2
Bootloader: I9505XXUFNC4
Knox warranty void: 0x1

My Wi-Fi router: Linksys WRT54G2

RubbaBand said:

Try to wipe data & cache
or try to flash another modem

Click to expand...

Click to collapse

I tried few different modems, like XXUEMK8 and XXUFNC9, both without and with NON-HLOS but they had the same exact problem. And this problem was at the very beginning on a clean install.

Could the modem be the problem? If so, how many times can I try to flash the modem? Can I ruin the NAND memory by flashing too much?