This has been added in the nightly release 0.65.1 and will be part of the full Wednesday release.
I did some testing with it and I’m excited to share that if the wifi connection goes down the machine will automatically reconnect, you just need to refresh the browser window to re-establish the connection from the browser.
I found the issue here…and it’s super pedantic. Apparently we can’t have space after the numbers or it will fail to load. 
I could work on making the FluidNC yaml parser more robust, but I think that the real long term solution is that we need to get rid of editing the file entirely. It just creates too many opportunities for something silly to go wrong.
Thank you for helping to find that. I will bump making the calibration process not require editing that file up on my todo list and I will now know what to look for in helping someone else with the same issue.
The good news is that the calibration process seems to recover well from a loss of WiFi connection in the middle of the calibration process (which I think is what you were running into). I made a quick video to show how I was able to get it to recover:
One last thing that I did was to turn my shop wifi off completely and double check that calibration works without an internet connection by connecting directly to the maslow wifi network and that worked too so that is an option also.