My first quick guess would be that your firewall prevents incoming connections. You have a lower download chance in this case. In the lower left corner of Phex you should see that little wall.
Try to configure your firewall to allow Phex as a server on the port that Phex suggests to you. Once you see incoming (Type IN) connections and the wall in the left corner is gone, you can assume that your firewall is configured correctly.

Limewire has some features Phex is still missing that allows automated firewall configuration and firewall to firewall transfers.

File not found can make sense, some people stop sharing the file once it is downloaded or very shortly after. Also candidates are not only spread through search but also through the download protocol, which is a bit slow in updating and spreading up-to-date information.

I hope you see better results soon. Try to raise your maximum parallel download connections overall and per file. Your connection speed can stand much higher values then the default.

Phex isn't automatically detecting its settings like Limewire, but instead it gives you more control on how and where to tune it. It requires a bit experience to find the best settings for you, but usually the results are worth it.

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