LB2120 Firmware update failure

So I managed to update my backup LB2120, I still need to find a good time to swap it with the in use one. Here's what I think the problem is (total guess btw):

The LB2120 downloads firmware over ftp or tftp, using UDP. It uses a trivial ftp client which downloads and does UDP manual retries when lost packets are detected. Each packet lost increments the error count until it reaches a pre-defined limit, and aborts.

I assume this because I know some popular open-source ftp clients have this exact same bogus design. They don't reset the error counts when a run of good packets is received, and the error limit isn't related to the download size, so the larger the file, the less likely you'll download it on a poor connection.

My connection drops packets, its in a bad area, even with a fancy antenna. Nothing I can do about that. I've tried numerous times, and the closest I got was 92% - so frustrating, but seen as bad as failure at 9% too.

This modem firmware is so poor, you need to reboot the device each time you want to retry firmware download. Secondly, on my backup device, the firmware update button doesn't even become available unless you have a SIM card inserted!!! Whoa! Its so stupid, its simply disabled in the HTML, so a trivial web page Inspect - I undisabled the button, which allowed my firmware update to proceed over my packet-loss-free WAN connection. Its bizare!  What sucks more is that the device wants to download its own firmware, no upload via HTTP from a browser, so there really isn't any other way to update this thing on a bad 4G link with no WAN.

Such a pitty there aren't many good cheap alternative modems to this.