I have exactly the same problem. We recently upgraded an older RUT950 to RUT9XX_R_00.06.06.1 now mobile does not automatically connect on startup anymore. Our other units in production running older firmware work fine, and this particular test unit worked fine also, until now.
I can confirm that changing the dial profile from NDIS to PPP makes it dial up, then when change back to NDIS is runs fine, it just doesn't start correctly on Boot.
UPDATE: It appears the script that starts an NDIS mobile connection up is either not being called on startup, or is failing (possibly because it's being executed before the device driver is loaded or some other trickery. I haven't ascertained why yet. The workaround is to start it manually after the router has booted using the User Scripts.
In the WEB UI: Navigate to System > User Scripts.
Copy and Paste this text directly above the line exit 0 at the bottom of the script.
Until this bug is fixed by Teltonika this workaround works for me so far.