Continuous operation is not always a malfunction. At low outdoor temperatures, an inverter unit may run for many hours straight.
When does it become suspicious?
When it never reaches the setpoint, the indoor temperature does not rise, or the compressor stays at maximum load.
Potential causes
Low available power, high heat losses, incorrect weather compensation, or a refrigeration issue.
What to check
Temperatures, power consumption, outdoor conditions, and the actual building load.