If you're worried about a tunnel connection and/or see missing transactions in your reporting you may want to monitor tunnel traffic.  

Many of our customers use the API (https://cohesive.net/dnld/Cohesive-Networks_VNS3-3.5-API.pdf - page 29 Describe IPsec Status) to monitor their IPsec tunnels.

If you run into any connection issues in the future, first find out: 
- Was there an IPsec log error on the VNS3 side and customer side before and during the outage? 
- Do you have Dead Peer Detection (DPD) enabled on the VNS3?
- Does your customer/partner have DPD enabled on their device?
- Did your cloud provider have a network outage in your region/zone?