"arp-scan -l" produces no listing on 19.10, works fine on 19.04

[Chris Green]

I have been using the command "arp-scan -l" to get e listing of local
systems for many, many years.

Suddenly, with version 19.10, it has stopped producing the listing.
It's even the same version of arp-scan that works OK on 19.04.

It does run, just no list of hosts/systems.

On ubuntu 19.04 (and earlier versions) I see:-

    chris$ arp-scan -l
    Interface: wlp4s0, datalink type: EN10MB (Ethernet)
    Starting arp-scan 1.9.5 with 256 hosts
    (https://github.com/royhills/arp-scan)
    192.168.1.1     00:1d:aa:c3:9b:e0       DrayTek Corp.
    192.168.1.3     90:1b:0e:06:bc:91       Fujitsu Technology Solutions GmbH
    192.168.1.4     b8:27:eb:b2:b2:fe       Raspberry Pi Foundation
    192.168.1.10    ec:08:6b:e2:f9:f6       TP-LINK TECHNOLOGIES CO.,LTD.
    192.168.1.20    00:50:7f:8b:35:40       DrayTek Corp.
    192.168.1.50    00:25:36:ae:52:9c       Oki Electric Industry Co., Ltd.
    192.168.1.96    2c:08:8c:cc:9a:9e       HUMAX Co., Ltd.
    192.168.1.98    18:d6:c7:9a:8c:8d       TP-LINK TECHNOLOGIES CO.,LTD.
    192.168.1.111   10:fe:ed:63:29:74       TP-LINK TECHNOLOGIES CO.,LTD.
    192.168.1.114   40:61:86:98:f2:41       MICRO-STAR INT'L CO.,LTD
    192.168.1.95    78:28:ca:fc:c7:84       Sonos, Inc.
    192.168.1.121   1c:1b:0d:60:9a:e1       GIGA-BYTE TECHNOLOGY CO.,LTD.
    192.168.1.105   6c:56:97:7b:26:f0       (Unknown)
    192.168.1.107   7c:89:56:d4:00:80       (Unknown)
    192.168.1.97    44:00:49:fd:3d:4d       (Unknown)
    192.168.1.110   b0:fc:0d:81:f6:34       (Unknown)

    16 packets received by filter, 0 packets dropped by kernel
    Ending arp-scan 1.9.5: 256 hosts scanned in 2.578 seconds (99.30 hosts/sec). 16 responded


.. but on 19.10 I see:-

    chris at esprimo$ arp-scan -l
    Interface: enp0s25, datalink type: EN10MB (Ethernet)
    Starting arp-scan 1.9.5 with 256 hosts (https://github.com/royhills/arp-scan)

    30 packets received by filter, 0 packets dropped by kernel
    Ending arp-scan 1.9.5: 256 hosts scanned in 1.965 seconds (130.28 hosts/sec). 0 responded


So where has my output gone?  The command obviously runs and there's
no obvious errors.  The one oddity is that it 'sees' twice as many
hosts/packets as before (30 versus 16 is just that occasional systems
don't always respond fast enough).  It's saying "0 responded" at the
end which is presumably why there's no output but I don't understand
what's wrong.

Any ideas anyone?

-- 
Chris Green