Proftpd Connection get random ECONNRESET

Hi I have installed in ubuntu 16.04 virtualmin gpl with proftdp as ftp server…

yesterday my client ask to mee about these errors in him ftp account…

I try to test the connection and the conection is ok but when I try to enter to more directories I have errors like this random…

ECONNRESET - Connection reset by peer GnuTLS error -110: The TLS connection was non-properly terminated. and sometimes the conections are fine...

I have the proftpd version 1.35 with this conf files:

proftpd.conf file:

Include /etc/proftpd/modules.conf
UseIPv6 off
IdentLookups off
ServerName “EU”
ServerType standalone
DeferWelcome off
MultilineRFC2228 on
DefaultServer on
ShowSymlinks on
TimeoutNoTransfer 600
TimeoutStalled 600
TimeoutIdle 1200
DisplayLogin welcome.msg
DisplayChdir .message true
ListOptions “-l”
DenyFilter *.*/

DynMasqRefresh 28800

MaxInstances 30 User proftpd Group nogroup Umask 022 022 AllowOverwrite on TransferLog /var/log/proftpd/xferlog SystemLog /var/log/proftpd/proftpd.log QuotaEngine off Ratios off DelayEngine on ControlsEngine off ControlsMaxClients 2 ControlsLog /var/log/proftpd/controls.log ControlsInterval 5 ControlsSocket /var/run/proftpd/proftpd.sock AdminControlsEngine off Include /etc/proftpd/conf.d PassivePorts 57000 58000

And Ihave CSF with 57000:58000 tcp and udp input ports open…

Could you help me about some info for fix it…