Alarm/Alert storms are known occurrences with products like Spectrum, UIM and eHealth. I'm aware of prevention measures you can take for UIM to detect and suppress potential Alarm Storms, I would suggest you raising a new ticket with the eHealth team to ask for best practices / guides to prevent this from reoccurring.
SOI can handle a large number of alarms however, if there is a flood of alerts in just a few seconds the SOI manager will go into a hung state and stop processing those alerts. We have an Idea open in the SOI Community for this scenario, I would suggest voting here:
SOI Alarm functionality to detect Alarm Storms - https://communities.ca.com/ideas/235736086-soi-alarm-functionality-to-detect-alarm-storms
The solution to this problem, would be to clear those duplicate / flood of alerts from the eHealth side and then recycle the Connector services. After this the alarms should be synchronized and the problem on the SOI side resolved.