BTW, there is a fairly recent posting about geotrace truncation.
If the odk:length wasn't specified in the original form, then there is a good chance that the original data has been (silently) truncated when it was submitted and saved in Aggregate. 
If you have physical access to the actual Android device you might be able to recover the original submission XML (which may have the full string)...
Aside, you can also calculate the area of a geotrace from within your form, using a calculation with the area() function.