When I sync my explorer+ to my PC the "off" option for send interval disappears. The only way to bring it back is to manually recheck my data plan on the device which goes through the activation sequence.
If you can't even see the Off selection in the list of intervals, then you should contact Garmin Support right away. Could be an account software problem, or firmware on the device.
I had a related problem earlier this year. After syncing Explorer+ to a PC my Send Interval would always be reset to 10 minutes, from Off (regardless of any other selected options). After extensive messaging with Garmin support, they replaced my unit with a new one (still under warranty). Turns out my issue was defective firmware, which in addition to resetting Send Interval was not updating its firmware during syncing.
