Correct. Using the Handy over Wifi means the script gets uploaded to Handy’s servers then sent back down to your Handy device. This can fail due to all sorts of issues, but most commonly because of Internet connectivity problems.
You can instead use the Handy over Bluetooth. HereSphere doesn’t support this itself though, which means running additional software.
There is a guide:
How to Host Scripts Locally for Your Handy - howto - EroScripts