I ran the OTA update twice on my supercid'd device successfully.
In opposite to what I could read here, my bootloader was unlocked before and still after the update.
The first time I ran the update I forgot to reflash stock recovery. The phone started updating and rebooted, but no changes had happened. After restoring stock recovery and downloading the update again, I successfully updated.
As I couldn't get root I restored Venom and downgraded my new hboot from 2.15 to 1.06.
Today I started a second try successfully without a glitch.
Basically I keep an untouched nandroid backup of every new rom installation on my local harddisk. This means in case of custom roms I do a nandroid before the first boot.
As this is not possible on stock recovery I change back to custom recovery after the first boot, doing my backup then. I'm just checking the needed boxes otherwise I only proceed during the setup - the complete customization is done afterwards.
In this case I restored a backup called 2012-08-23--08-18-16_htc_stock_2.31
Stock here means: No apps, no customizations, no nothing, simply: stock and supercid.
After that was done I restored apps with Titanium.
That's how it worked (pretty simple) Maybe this will help you find some reasons for what has happened to your devices.