Do the activities show up on the watch, on the Last Activities widget screen? If not, then you perhaps did not save them. You can also connect the watch to a computer by the USB cable and browse the folder //GARMIN/Activites to check whether the activites are there or not. Some older models tend not to clear old unused activites and hence not letting any free space, after a longer time, which could result in the inability to store new files. Cleaning the Activities folder over the USB cable would help then too.
Also have a look at the Sync Audit in Garmin Connect on the phone. You get too it in Menu » Settings » Device Sync Audit (at the very bottom) - it may perhaps reveal some details or errors during the sync process.
