GPS recording at interval +1s

Thanks for digging down into it!

I just checked and the code that converts NMEA data into lat/lon for Espruino does use doubles, so I don't think that is the source of your inaccuracy.

The NMEA speed value is actually reported in the GPS event, I guess it's just not logged by the gpsrec widget. With some minor changes to the JS you could export that value though, if that's what you're specifically interested in?

I guess if this is reproducable it'd be pretty easy to log the full NMEA sentences, so you can check those and see if there are problems?

Does the GPS Recorder 0.21 affect updating, retaining, or using GPS time

It doesn't, no... Literally all it does is choose which GPS fix to record, but it doesn't modify them.