I’ve experienced the same stalling you’re seeing with the plugin (both free and premium versions), as well as the % bar going well over 100% by the time it finishes. I’ve run through a migration three times and each time had to resume it at least 20-30 times for it to finally finish.
This is a major pain, no doubt about it, but I’ve not noticed any duplication of records and the plugin seem to bring over everything it says it will. I, too, reached out to the plugin author and didn’t get much help about the issue – but he was responsive at least. What I did was run the import and tail the progress log directly since the UI log window doesn’t update:
tail -F wp-content/uploads/fgm2wcp-progress.json
I essentially waited at least 5 minutes before figuring the process stalled, then I reloaded the plugin page and resumed again. Rinse/lather/repeat… for as long as it takes for the plugin to complete the migration. It seems to progress about 5% each time, at least for the migration I did.
If I had lots of time on my hands, I’d put a lot more logging in place so there’s a sense for where the plugin just gives up, times out, or whatever. It’s gotta be something that can be mitigated in some way.
For all its failings, this plugin did save us hundreds of hours of work manually copying almost 500 products from old site to new. I looked at other plugins but they don’t seem to have anywhere near the breadth this one does. I just hope it can be strengthened in the weeks/months to come, so it can literally be a one/few-click progress, not 20-30 times that.