No SMS received by device

I am prototyping an asset tracking system that uses a SMS as a trigger to send data to the Hologram Cloud.

The SMS is being sent from the Hologram dashboard or from a python script using the API.

It worked fine a few weeks ago, but today I have noticed that no SMSs are making it to the device.
I have tried putting the SIM card in a cell phone but still no SMS came through.

SIM is registering to the network fine, and ROAMING is active.

On the dashboard log, the messages are visible but not SMS delivered message is being shown as it used before.

I tried to send several messages but non made it.

What could be the problem? Could this be a mobile operator block?

I tried using two networks that are Go Mobile and Vodafone MT

These are Maltese operators.

I am having the same issue of SMS is sent form dashboard and nether the sms arrived at device and not confirmation updated on dashboard. This has happened so many times.
I have been same situation few times in last week.
Very unreliable SMS delivery system,

My operator is Rogers Wireless Canada
Also facing same issue on AT&T in USA
Using sim on Nova and phone

No results