Hints regarding capture of the pcap file

see if you’re capturing the packets using tcpdump command without any filter then your file size will increase drastically in 1-2 minutes your workspace will be hanged
so I would suggest reading about filters.
since your server is running on 8081 so do capture packets on port 8081 || 8082 ||8083
see this for reference
why 8082 and 8083 (check your vsftpd.confi file)

To get very small pcap files you can get your public ip address from vsftpd.log and filter the traffic in tcpdump using src flag followed by your public ip addr.