I'm having exactly the same problem.
I did a couple of prints this morning and decided to update the firmware. Now on 5.2.11.
To be on the safe side I did a single auto-level then went to print the same object (a very simple disc with two holes in it). It did its usual little pile absolutely fine - but then nothing. The nozzle was touching the glass plate and nothing was coming out (because the nozzle was being blocked by the plate).
I've tried several attempts at auto-levelling since, with the same effect.
Something is very wrong.
I've also noticed that the progress bar on the base-heating and nozzle-heating doesn't work any more (although they're both heating up as expected).
Unfortunately, I don't know what the previous firmware version was, but I need to go back to it as a matter of urgency - is there a mechanism for reverting to my previous version?
This is on an Ultimaker 3.