String variables takes long time to populate on Web interface or Mobile App

I have a project where i use a GSM modem, am using gammu in order to get data off the modem (network name, signal strength, balance, credit expiry date), i am fetching this through a shell script that run everyhour and export the output to files, and then on the Item level i use exec cat the file to get the value.

It is noticeable that Number items i created populates fast (when page is refreshed or app is opened like the credit and signal strength, while the Network name and expiry date) takes around a couple of seconds (sometimes more ) to populate.

once populated, if i refresh the page it gets blank again, has someone experienced such an issue ?

//GSM Balance
String GSMName		"Network Name:"		<none>	(GSM)	{exec="<[/home/pi/meshx86/scripts/ussd/ name:10000:]"}
Number GSMBalance	"Balance: [%.3f KD]"	<none>	(GSM)	{exec="<[/home/pi/meshx86/scripts/ussd/]"}
String GSMExpDate	"Balance Expiary Date:"	<none>	(GSM)	{exec="<[/home/pi/meshx86/scripts/ussd/]"}
Number GSMSignal	"Signal Strength [%.1f  %%]"	<none>	(GSM)	{exec="<[/home/pi/meshx86/scripts/ussd/ signal:10000:]"}