Sure thing it is a network connectivity issue. The most common cause of network degradation is the overload in the CPU or Memory of your instance, so you need to review your VM CPU and Memory utilization.
To check it, open the cloud console then Compute Engine and choose VM instances, then click on the three dots of your instance and select View Monitoring CPU and Memory utilization charts. Look for the time frame when the issue happens and make sure that your instances have enough memory and CPU power to support the load as it is demanded at top hours.