Bug#922307: proftpd-basic aborting transfer

[david at daveserver.info]

Package: proftpd-basic
Version: 1.3.6-4

Some users (generally a distance away from the server) when attempting to upload files larger than 2mb the server closes the connection. Smaller files upload fine.
Error as seen in the log (/var/log/proftpd/proftpd.log) for each attempt:

notice: user testuser: aborting transfer: Interrupted system call

The problem does not exist with the same configuration in version 1.3.5b-4.
Added configuration items from stock.
Various files in /etc/proftpd/conf.d/* containing

DefaultRoot /home/UserName/Website UserName
DeleteAbortedStores on
AllowStoreRestart on

and in proftpd.conf
RequireValidShell off
MasqueradeAddress insert.wan.ip.here

This is on an up to date 14/02/2019 buster installation
Seems to be the same problem as expressed here.
https://github.com/proftpd/proftpd/issues/668#issuecomment-357406734 (https://github.com/proftpd/proftpd/issues/668#issuecomment-357406734)