Track logging currently works like this:save current position + elevation + timestamp every N seconds to memory every M seconds dump the complete in memory log to file (and replace the last used file) By default N =1s and M = 10s, both can be configured in "tools" in the logging menu. So when something goes wrong (the phone crashes, the power runs out, etc.) you should have the complete log without few seconds from the last dump.
There is currently no way to resume a log,
but this can be added.