I have a Tom Tom Via 620. I have owned it for about 6 years and have always found map updates a nightmare, without exception. I avoid them as long as I can. I have a selection of Micro SD cards of varying sizes from 4GB to 32 GB and not a single one of them is accepted. They all result in a message saying the card does not work, all except the 4GB card which says that the card is empty, whatever that means. I check on the acceptable SD cards page on the web site and my model is not listed anywhere.
In the meantime, I have managed to download the latest update but the device simply will not connect to my Windows 10 PC to load it. I have followed all instructions including hard resets, PC restarts, driver re-installations, the list goes on. I use the provided USB cable. Reading similar experiences in this forum and elsewhere, one wonders how Tom Tom can still be in business.