I can't say I have seen this too much, but I do feel like I can recall instances where Jobs from ServiceM8 seemed to take an overly long amount of time for them to make their way into my calendar.
First question I would think of is if you have checked on Google Calendar and not just your device.
Assuming this is not the case, it really just comes back to ServiceM8 interfacing with Google on this front, which we are all removed from (and I don't think there is much that can be done with heavy documentation of it happening, which can be hard and problematic).
As for a potentially more reliable and paid service, that should be something we can explore once we have our
PortalMEin platform up.