I was not able to replicate your issue, the device responded to SMS after update via message.
Since you have a local RUT240 for testing, could you login to router via SSH, execute logread -f command and see, if any messages are generated regarding the event in the terminal?
Unfortunately, modem module firmware update is not possible over SMS and the procedure requires a secondary internet source, either wired or wireless.
SMS not working may be due to the gap between firmware releases and possible migration issues.
I would like you to check locally, whether a device reset to factory default settings (login to the WebUI, navigate to System -> Backup -> Restore default settings) does solve the issue and SMS are received?
Otherwise, it would be helpful if you could provide a couple of troubleshoot files from your device:
- One with firmware 7.02.7, generated after sending a couple of SMS to the router.
- Another, after update via SMS to 7.03.3, also generated after sending a couple of SMS to the router.
To generate the file, access router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there. The logs in the file might provide more insight into the issue. Generated files can be attached by editing your original question.