Hi,

One of the boxes is a WD NAS runinng NUT 2.6.4 (I can't really upgrade it, and WD seems pretty conservative in terms of their updates). The other one is an RaspberryPi running ARM Linux and the latest NUT 2.8.0.
When connecting from WD NAS to the Pi with upsc -l <ip-of-pi> I'm getting:

Apr 04 10:07:58 PiWM upsd[4100]: listening on * port 3493
Apr 04 10:07:58 PiWM nut-server[4100]: Connected to UPS [usbhid]: usbhid-ups-usbhid
Apr 04 10:07:58 PiWM upsd[4100]: Connected to UPS [usbhid]: usbhid-ups-usbhid
Apr 04 10:07:58 PiWM nut-server[4100]: Running as foreground process, not saving a PID file
Apr 04 10:07:58 PiWM upsd[4100]: Running as foreground process, not saving a PID file
Apr 04 10:09:15 PiWM nut-server[4100]: Unknown return value from SSL_accept: Success
Apr 04 10:09:15 PiWM upsd[4100]: Unknown return value from SSL_accept: Success

On the WD NAS side I'm getting the following error after a considerable delay:

Error: SSL error: error:1409E0E5:SSL routines:SSL3_WRITE_BYTES:ssl handshake failure

That's a recent-ish development as the setup used to work up to some unspecified point in the past (I'm not sure when exactly it stopped working, as I only noticed today that the NAS didn't connect anymore).
The other commands such as upscmd do work correctly, so this seems to only affect upsc to the best of my knowledge.

I tried regenerating the cert file according to the docs in case it was an expired cert, but that's not it. Similarly, fiddling with DISABLE_WEAK_SSL didn't yield any results.

I think this might be related to: #246 and #202

I'm not sure what else to try other than downgrading the server on the Pi and seeing at which point it starts working. Any pointers?