Nut upsuser - Dec 2019 - NUT not shutting down one of three UPSs (sometimes none of them shut down)

I have three APC SmartUPS 5000s. Two of them are AP9617 and one is AP9619.

I have a RS-232 connections from my monitor host to all three. All three
report status and give information.

One of the two AP9617 - ups3-1 - does not shut down when FSD is sent. It
did when I first set this system up a year or two ago but it's stopped
doing so since then. Resetting the management interface does not change
anything.

This is all that shows up in /var/log/messages on the host that is
connected to the UPSs and running the full NUT suite:
Dec 25 08:00:26 [redacted] upsd[9800]: Client upsmon@[redacted] set FSD on
UPS [ups1-1]
Dec 25 08:00:26 [redacted] upsd: Client upsmon@[redacted] set FSD on UPS
[ups1-1]
Dec 25 08:00:26 [redacted] upsd: Client upsmon@[redacted] set FSD on UPS
[ups2-1]
Dec 25 08:00:26 [redacted] upsd: Client upsmon@[redacted] set FSD on UPS
[ups3-1]
Dec 25 08:00:26 [redacted] upsd[9800]: Client upsmon@[redacted] set FSD on
UPS [ups2-1]
Dec 25 08:00:26 [redacted] upsd[9800]: Client upsmon@[redacted] set FSD on
UPS [ups3-1]

The other two do shut down... most of the time. I've now observed two
occasions in the past 6 months where none of them do so.

All three UPSs report the same Application module and APC OS.:

Application Module
Name: sumx
Version: v3.7.2
Date: 02/02/2010
Time: 19:08:16

APC OS (AOS)
Name: aos
Version: v3.7.3
Date: 02/02/2010
Time: 17:05:14

Yes, these are old UPSs and I've requested money to replace ups3-1. Of
course, that won't help if NUT doesn't shut down any of them.

Any advice would be appreciated.

thanks,
nomad
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On Wed, 25 Dec 2019, Lee Damon wrote:
> I have three APC SmartUPS 5000s. Two of them are AP9617 and one is AP9619.
> 
> One of the two AP9617 - ups3-1 - does not shut down when FSD is sent. It
did
> when I first set this system up a year or two ago but it's stopped
doing so
> since then. Resetting the management interface does not change anything.
> 
> The other two do shut down... most of the time. I've now observed two 
> occasions in the past 6 months where none of them do so.
If you swap the physical units ups1-1 and ups3-1, does the problem follow the 
hardware, or does it stay with ups3-1 ?

Roger