Perhaps you could be a bit more specific, or give some actual details;
You may as well say "It doesn't work, now how do I fix it?"
What specific version of Windows OS are you using?
What specific version/build of FlashFXP were you using?
What anti-virus and/or firewall software/version are you using?
What is the server software/version?
What protocol are you connecting to the server with? FTP, FTPS, or SFTP.
If connecting using FTPS or SFTP then what cipher and strength, etc is being used?
(some ciphers are much faster than others; the default cipher order is based on strength and not speed.)
With SFTP latency is also an major issue, so what type of delay do you see when pinging the server IP?
Many performance changes were just recently made in 18.104.22.16852. Along with these improvements we also discovered some unexpected performance issues in the SFTP/encryption library we use (SecureBlackBox), Specifically I found that the es[128/256]-gcm and chacha20-poly1305 ciphers are slower than other libraries.
With SFTP you can adjust the cipher preference/order via the Site Manager > SFTP Tab.
With FTPS you can also adjust the cipher via the Site Manager > SSL Tab,
but you need to enter the cipher string in the OpenSSL format which is a bit more complicated.