Spresense LTE expansion board may take longer to connect

Developed by arduino IDE.I'm looking at the sketch example LteScanNetworks.ino.
At the earliest, it takes about 10 seconds to connect and attach succeeded, but
If it is long, it will not connect for more than 20 minutes.
SIM is using truphone.Docomo's 4G smartphone has good reception.
Is there a possibility that the connection will be faster if I use the domestic SIM?
Is there any procedure to speed up the connection?
The LTE LED on the expansion board is flashing erratically.
Signal Strength is around -90.

A little over 2 seconds at lteAccess.begin lteAccess.attach takes from 7 seconds to possibly more than 20 minutes.
Is there a way to timeout if the connection is unstable?

This is not the first connection.
Verified the power supply.

Thank you for your cooperation.

Additional
Maybe this is the situation.
https://www.soracom.io/blog/sim-activation-cellular-modem-fix/
Does it slow down when the cache of network information is cleared for any reason?
There are some countermeasures, but how do you set it up from arduinoIDE?

It says that scannerNetworks.getCurrentCarrier() gets the network carrier name, but it returns truphone which is APN, not carrier docomo, etc.
Is there a way to check if you are connected to docomo or softbank?