Baffled why M8 won't flash OTA topic

Bit of history here :

I had rooted and flashed TWRP etc prior to 4.4.4

Once 4.4.4 came out OTA nagging annoyed me, so i went back to stock, stock recovery, unrooted but still S-OFF running Super CID.

4.4.4 then took via OTA no problem.

Nothing has changed on phone since. Yet lollipop OTA won;t take (Red Exclamation).

I'm on 3.28.401.9 (shown via settings)

Bootloader shows :

*** Software Status: Official ***
*** UNLOCKED ***
M8_UL PVT SHIP S-OFF
CID-HTC__001
HBOOT-3.19.0.000
RADIO-1.22.21331147A1.29G

As far as i'm aware, i'm on a fresh flash of an OTA upgraded KitKat, with stock recovery?

Any ideas why new OTA won't work?

Thanks in advance.