Backup Scheduler unable to perform backups

Experiencing the same problem described in this support post:

https://www.ads-software.com/support/topic/backup-not-working-7

Namely, the following is displayed:

The process is still in progress for this backup (begun May 6, 2016 at 15:34:50.).

The ZIP creation is in progress (0/0 files has been added in 1 zip files and the current size of the zip files is 0.00 KB).
Cancel this process

Please wait, a backup is in progress for 12 seconds! Wait until 45 seconds for an automatic restart.
This error message may also be generated if the chunk size is too big: try first to set the chunk size to 1Mo in order to avoid any memory saturation of your server and then increase it slowly...

Have tried setting both of these values to 1 MB but no avail:
maximum zip file size (in MB, namely the chunck size):
maximum size of allocated memory (in MB):

Site is running WordPress 4.5.2.
PHP Version 5.5.35
Please let me know if you need any PHPinfo values.

Anything else that can be tried?

https://www.ads-software.com/plugins/backup-scheduler/