Offline malfunctions are a common status, but the cause and resolution is different based on the type of device. It is not all the same cause. Ultimately what it means is that the device is having trouble communicating, but different devices have different communication methods.
For sensors and Z-wave devices we have a guide below going over the common causes. These are the most common offline statuses, and for sensors it often a combination of factors, such as range or attenuation compounded by lower battery levels (even before a low battery status).
For Ecobee, it has been a common report that Ecobee reports offline intermittently. This usually appears to be due to intermittent wifi loss on the ecobee thermostat. This is a back-end integration where ecobee sends Alarm.com those statuses. Quick drops and restorals can happen for various reasons. Do you have multiple access points or a mesh wifi system? What model router do you use?
You can turn off all malfunction notifications by editing the system actions to watch notification in Alarm.com.