Nut upsuser - Oct 2019 - Communications with UPS denchi@localhost lost

Hi,

I always had problems that my Smart-UPS 1500 had "hickups" with nut:
Connection would get lost, just to get restored seconds later again.
This resulted in annoying log entried and console messages but wasn't
too critical. For a few days, nut doesn't detect my UPS at all any more.
I get the console messages:

Broadcast message from nut at server (somewhere) (Tue Oct 29 04:54:50 2019):

UPS denchi at localhost is unavailable

However, my UPS is connected via USB as it has always been and is
detected by Linux:

# usb-devices
[...]
T:  Bus=01 Lev=01 Prnt=01 Port=04 Cnt=02 Dev#=  3 Spd=1.5 MxCh= 0
D:  Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
P:  Vendor=051d ProdID=0002 Rev=00.06
S:  Manufacturer=American Power Conversion
S:  Product=Smart-UPS 1500 RM FW:617.3.I USB FW:1.5
S:  SerialNumber=AS0351210216
C:  #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=30mA
I:  If#=0x0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=00 Prot=00 Driver=(none)
[...]

When I call the driver directly:

# /lib/nut/usbhid-ups -a denchi
Network UPS Tools - Generic HID driver 0.41 (2.7.4)
USB communication driver 0.33
device->Product is NULL so it is not possible to determine whether to
activate max_report_size workaround
No matching HID UPS found

Since the entire log is large, I post the output of "upshid-ups -a
denchi -DDDDD" here: https://pastebin.com/3AMcmD7i

Linux radix 4.19.0-6-amd64 #1 SMP Debian 4.19.67-2+deb10u1 (2019-09-20)
x86_64 GNU/Linux, nut 2.7.4 (Debian version).


I am afraid this is a bug in usbhid-ups. Any idea the issue can be
traced and fixed?


Thanks,
Luke