Plusnet router, BT discs Solis wi-fi disconnecting

[#1]

Hi, I have been using the Plusnet Hub One router with BT wi-fi discs successfully for about a year and all connected devices work great connecting and reconnecting except one. My new Solis inverter wi-fi dongle which is used for logging solar generation and uploading to a web page is connected daily and for the past 2 weeks has failed to reconnect on a Friday morning. Note; the Solis inverter powers down every day at sunset so the wi-fi dongle has to reconnect daily at sunrise when solar power is generated to power up the inverter.
The dongle has to connect to the router via the BT discs but I don't see a way to change IP lease periods in the BT Whole Home wi-fi disc app and the app is not the DHCP server either so that would contradict the Plusnet router DHCP lease period if it could.
At first I thought this 7 day failure to reconnect would coincide with the Plusnet router IP lease period but after checking the settings that is set to 1 day.
I've checked the admin page for the Solis wi-fi dongle and there are no settings for lease or connection period as far as I can see.
Has anyone had a similar issue with a wi-fi device and maybe got any ideas where I can look next to resolve this 7 day reconnection issue?

[#2]

@Moovrr 

What makes you think that it has anything to do with lease periods? These simply automatically renew if a device is connected or if the device is not active at the time it will reconnect the next time the remote device comes on line. The fact that the Solis is off line at night is no different to any other wireless device being switched off for a period.

How do you reconnect on a Friday morning? Do you have this problem with any other device? If not then I  would start by looking at the Solis settings and/or talking to Solis.

I have an ABB solar inverter with presumably the same setup, that is, it has it's own built in web server to which, in my case, it reverts during daylight hours if there's no connection to my network. This is identified by the colour of a LED on the Inverter. Is this the same for you?

[#3]

Hi Baldrick, thank you for your thoughts and questions.
I only considered the lease period because of the fact that for 2 Fridays in succession the Solis wi-fi dongle (aka data logger) has failed to connect and thought it must be a time-out based issue. But you're reasoning is correct that any other wi-fi device switched off manages to reconnect when back online ok.
You are right that there may be something I haven't seen yet in the web server config page for the dongle that affects the connection time but I have been through it thoroughly.
I have no issues with any other device so it all points to the wi-fi dongle which doesn't need reconnecting on any other morning when the inverter powers it up except Friday!
When it fails to reconnect I connect to the dongle wi-fi directly and go to the web admin page and follow the setup wizard to re-enter the connection settings for the Plusnet router, that seems to connect up again for another week...maybe...
Your inverter sounds similar but maybe your wi-fi is more integrated in the unit, my dongle is attached to the port underneath the unit so I don't get any status indicator lights anywhere. Perhaps a maintenance engineer level access to the inverter would see more about the wi-fi connection, TBD.

[#4]

@Moovrr 

So when you log back in using the Solis IP address  and go to the Plusnet settings have the previous settings been cleared down and you have to reenter them? If so try logging in the same way now and see if they are retained, which is what I would expect. Then try again next Thursday to see if it’s the same. 

If the settings are getting reset on a Thursday/Friday morning I would assume that Solis is resetting  the interface for some reason.

My inverter is monitored by ABB. I don’t know if Solis do something similar and are resetting it.

[#5]

Yes as you said when I go back in using the Solis IP I can see the router settings are retained, but on a Friday morning they have been wiped and I have to re-enter them.
I've tried calling Solis and their automated call distribution isn't accepting my number selection so I've left a message for them to contact me, I'll find out if they are resetting my web server for some reason. Thanks for your help, I'll let you know what response I get.

[#6]

@Moovrr 

To my mind this shows that the settings are being cleared down by your Inverter. I'm not aware of how this could be done by your BT WiFi disks.

It will be interesting to hear what Solis has to say.