NEO KEYM8 1.4.0 – Unit Transfer failed 45127, dimmers program OK

(new user here sorry if this post is in the wrong place, pls direct me if that's case tnks)

I can't save programming changes to any of the NEO key input units on my home C-Bus network. Changes save to the Toolkit database, but the transfer to the unit fails every time.

Details:
- Units: 13 x KEYM8 8-gang NEO key input units (5058NL), all firmware 1.4.0, addresses 101–115
- Error when saving to the unit: 45127 "Unit Transfer failed"
- Earlier, when opening units: 3036 "Failed to load unit programming. Network Scan is required"
- Reading from the keypads works; only writing fails
- Dimmer units (DIMDN4, firmware 1.3.0) on the same network program without any problem
- Same result on two different PCs, with Toolkit 1.16.3 and Toolkit 1.19.5
- Network diagnostics are healthy: voltage good, 1 burden, 2 clocks
- Interface: PCLOCAL4 DIN Rail PC Interface (firmware 4.2.00), network 254
- The "Open Unit in Classic" option is greyed out for these keypads

Questions:
1. Is there a known issue programming NEO key units on firmware 1.4.0 with these Toolkit versions?
2. Is a firmware update available for these units, and how is it applied?

thanks for your patience-new user trying to get across all this.
(I inherited this setup I didn't create it so can't know if a new issue or old one)
OldDogNewTrick