After a bit of searching I've found some references to JEFF.BIN file, always regarding Drive Series devices. There will be another file of same name in the internal memory of the device, also in a hidden folder named JOURNAL but it's likely got some readable bytes. Anyway, I don't think it's got anything to do with the problem this device is having, more likely JEFF.BIN is maybe some java-related performance enhancing file specific to Drive series but there may be other recent devices which also have it. It seems it's likely always created on the SD card by Ldr.bin's initiation and it's size is consistently exactly 32 KB (32,768 bytes) albeit all zeros. The original file on the device is also 32KB and mostly just zeros with minimal readable data referencing other files on the device.

So for your Drive 40 attempting SD flash, Ldr.bin is being initiated but is unable to go too far and txt commands aren't being executed. When there's no files named Last_ID.bin and Update.log created in the card then the flash has failed. It seems that because this device has lost it's UID and HWID and has likely flash damage across multiple regions that it's not a candidate for recovery. Maybe it could be JTAG'ed by Garmin to reprogram the flash chip however they only offer a 'one for one' replacement service at a prohibitive price. Sorry but it might be only a candidate for parts now because it's very likely this is a hardware failure.