System Memory Reset and SIM locked

I have problems with my iPad Pro 10.5

Sometimes when I first took my iPad in the morning, it says that the GSM part is locked and I have to insert my SIM Pin.

In the data of the diagnostics is every time a data set entry "SystemMemoryReset+date and time.ips".

Inside this ips there is a line:

"eventReason" : "User reclaimable memory dropped below the limit. User reclaimable current: 73%. User reclaimable minimum: 75%"

Where the number of the 73% could be different, but always below 75%.

At present my iPad is running at iOS 11.2.6 but I have the problem already with older versions.

What's going wrong?

Is there a problem with the RAM in my iPad?