While training at a Myzone gym, your workout uploads are completely dependent on your gym's Myzone in-club system-- this is true whether or not your mobile app was open and streaming your heart rate!
Missing or Delayed
This is most likely due to the in-club system being offline (usually identified by a cloud with a red X on the screen): 
This is easily resolved by a staff member on site, and once restored, your full workout should appear on your account shortly after.
Gaps
If you have small or large gaps in your graph, it is likely that your facility's clock is set incorrectly on the in-club system. Let a staff member know ASAP so they can correct the issue on-site, and try keeping your mobile app closed while at the gym to prevent discrepancies when possible.
Belt not connecting
If you noticed the belt's reading of your heart rate drop out, drop very low, freeze, or "search," then it is likely your belt struggled to capture this workout. Please see our troubleshooting guide for the MZ-1, MZ-3, or the MZ-Switch.