It's because of the recent WNRO which is discussed at length
here TomTom have released a new official navcore for your Go 530's (NC 9.541) which addresses this and other minor issues...but you want to continue using the Truck navcore which hasn't been fixed. So you can either do a hard reset of the device/or use FastActivate every time you need your satnav...or you can install the official navcore for your devices and have no more problems.
It's up to you but I know which option I'd choose...