Just a small update.
Still using the lock without problems, but by adding it through my old (my fathers now) phone.
There is a Mobile Device Management system from work on my phone that could be the problem, but our IT guy is only 2 mornings every week in the building and as a truck driver, I am usually not.
Still to be continued!
@welshbryn are you any further?
Hi.
I didnt go for the new gen lock because id have had to pay an upgrade fee and it was basically the same as buying a new one. They sent me a replacement and touch wood its been much better
Ios seems to be fixed
Thanks for the update
Unbelieveable
Spoke too soon. You jinxed me 
Lock went offline yesterday. I spent hours and could not get it to work. Total factory reset, turn off 5g turn off AX mode and smart connect on my router, unplugged all hubs i don’t “need” to pair to.
Nothing. Will not connect back to matter.
Sorry! 
But strange…
Are you trying to connect it via WiFi or Thread?
Matter. Any tips?
I got the lock new (as a replacement because the old one died after 6 months)
It connected immediately out of the box.
The old lock dropped offline every few days. This one has been rock solid until yesterday
I’m asking because “5g”, “AX mode” or your router has nothing to do with Thread…
The lock connects directly to the Thread border router in your SmartThings hub. No WiFi router involved!
Add some Thread routers - like the Eve Energy plugs or Nanoleaf Essentials Matter over Thread bulbs - to your network. It’s a mesh network after all…
And make sure that the WiFi module in your lock is turned off!
Interesting you say I will certainly try turning off the wifi module.
Its not something Nuki have suggested but they and Asus (router manufacturer) have said that 5Ghz. AX mode and Smart connect are all things that can affect IOT devices and its been part of the Nuki suggestions to turn them off to remedy it the matter connection.
They even said pair my lock and hub to a hotspot to test it.
I have zero issue connecting any other matter device and ive never changed any router settings. Only Nuki is the issue
Gave it a go. No resolve im afraid
Afraid. Deleted and reset the lock and started as if it was new.
Same issue 
Do you have any other Thread devices in your network?
Contact Nuki support here
I have Tado x and Govee things that are all matter but none that are Thread i dont think.
Ive contacted Nuki Support. Its been going on since last year when i got the lock. They say the same thing every time.
Resat art the device, put it in maintenance mode, turn off 5ghz,
Turn off any other hubs in the house and wifi repeaters.
Then they ask for proof of purchase and proof of warranty. Then they ask to delete the app and reinstall
And ask what version of ios your on.
This goes around in circles time and time again every single time they email me they ask for proof of purchase - their customer services are a total joke
Today however i found a solution and it worked
I factory reset my lock, reinstalled it like its new.
Tried smartthings first - no luck. Tried apple HomeKit, no luck.
Tried maintenance mode, no luck. All this time my door was open and the lock was unlocked.
I locked the door using remote access through the app and then went back to the matter menu. I added it to Apple Homekit first and it worked immediately.
I tried smartthings straight after and that worked too.
I cant see how but with the door locked it worked.
Fingers crossed this wont disconnect again for me to have to test that theory.
Give it a go
So after much back and forth with Nuki. They have now said the ios18.4 issue ONLY affected adding the lock to HomePod and said it had no impact on SmartThings
I proceeded to then copy emails they have sent in the past “problem solving” emails where they exclusively blamed ios for not pairing to smartthings and even washed their hands of the issue saying its an apple
Issue contact them.
They have now told me that there is a matter issue but its not affecting all users.
I asked if thats a known issue then why didnt they just reply with that in the first place instead of taking almost a month of back and forth asking the same questions on each Occassion and repeating ALL of the same steps ive used for the last 12 months of this issue existing.
Their reply - They sent me a £10 voucher.
Nuki clearly cant answer why their lock drops offline or why it takes days to pair back and fails to pair with ANY matter hub not just SmartThings.
They seemingly dont know whats affecting pairing and by the time you actually get a reply from someone who does they offer you a voucher.
Great
Did you ever figure out the difference between WiFi and Thread?
I know the difference. Its a different protocol and lower power. However i was following the advice of Nuki to try make it work. The same advice other users on here have had
Knowing the difference between the two has not resolved the issue at all. As ive said previously i have no issue with any other of my devices in my smarthome accross any of the platforms i use
Several smarthome products recommend turning off 5ghz or smart connect features
Nuki even suggested turning off all Ipv6 settings despite Matter devices requiring this feature
How many Thread routers (not Thread border routers) do you have - AC powered Thread devices like the Eve Energy plug or Nanoleaf Essentials bulbs/strips?
The last time someone had these issues, I recommended to place a thread router near the Nuki lock and that solved the problem for good!
I have at least four thread routers in every room (easy when every light is a Nanoleaf device). Even only one device per room would create a rock solid Thread mesh network.
You know, your lock should have one or two alternative paths back to your Thread border router (SmartThings hub). It’s all radio signals after all…
Ok i see. I have no other thread devices but all of my hubs are all within 4 foot of my door with no obstructions at all. It really does seem to be a product issue and something in the way the device is recognised
However ive tested again and deleted my device. It does pair when the door is locked but fails when open.