I have also similar problem. I have problems starting the car and when it does not start from the first time, it gives "Alarm not available" error. There are sometimes other errors displayed about full DPF filter (have it removed) and also Check gearbox (when it was displayed, gearbox actually didn't work properly).
Now started to use a trick in starting. When inserted a key, waiting for glow plugs icon to turn off, remove a key and put it in once again, wait second time for glow plugs to pre-heat and once the icon is off, starting the engine. Then engine starts well, no errors displayed, no problems driving. The only problem remaining is alarm now beeping twice when arming.
What could be the cause? Glow plugs were changed around a year ago. Braught Alfa to electrician for diagnostics, but it could not say anything specifically whats wrong. Said only, that nozzles seemed to working wrong and should be checked. However I have a feeling that it should be something with electricity. Could the problem be weak battery (changed 3,5 years ago).
Wanted to have some suggestions otherwise thinking of going to do diagnostics at an Alfa dealer that is not a cheap thing probably
One more thing I remembered - when the problems started, steering wheel controls stoped working and also radio now turns off as soon as ignition is turned off, not when key is removed.