Unable to program brand new eDLTs

I have two new eDLTs. I connected one to my network, and it appears after a scan. However if I try to open its properties from the network using TK I get this "Failed to load unit" error:

and then this after OK ("Object reference not set"):

I am able to readdress the unit (same error afterwards). I have swapped to the second new unit which fails the same way, and also swapped it with a working eDLT on the same network to prove the cabling is OK.

If I transfer to DB, I get this error:

.. but the unit does get added to the DB. If I then try opening the unit from the database instead of the network I get the same errors as if I tried opening it from the network. This to me suggests that TK is able to extract the configuration "blob" from the unit OK, but it is corrupt in some way?

Interestingly TK doesn't show me the unit's serial number so something quite basic is failing (but like I said it allows me to readdress it so some stuff is working). A diagnostic scan sees the unit OK but voltage comes back as "unknown". Both units are similar serials so presumably same batch, both are 1.8.0 firmware.

Most of my tests were using TK 1.18.2 but I installed 1.16 to test (same result). SLCC also can't open the unit from the network.

Are these both faulty, or am I doing something wrong? (Can I revive them?)

 

I have downgraded the firmware in one of the units to 1.7.0. Initially it made no difference (double-click in TK network view, same error). But after a rescan it worked, almost like the issue is in TK not handling firmware 1.8.0 rather than anything in the unit itself?

Questions:

1. Is this the right fix?
2. Can I trust the units?
3. Is there anything in 1.8.0 that I (or the unit itself) might need?

 

I'm guessing this is because eDLT 1.18 requires TK 1.19?

Is there a reason why 1.19 hasn't been announced here in the forums? (Or am I just blind?) Navigating the =S= website is messy so I've tended to come here to find out what version is the latest,