That's perfectly normal, all mine do the same - and I actually use the IMEI to identify the units they are built-in.
But there's no need for the printed number on the board, mine connect to a PHP/MYSQL database, and automatically create a new entry if the IMEI number isn't already in the database thus self registering.
As for not registering, are you trying to leave it permanently connected?, because after a while the provider will disconnect you.
One of mine has recently flattened it's battery, it was on long term test running from a single (second hand) 18650, uploading data every 8 hours (normal usage for the intended application would be weekly) - it managed 378 uploads, before the battery was too low for it to continue.