This is a common misunderstanding, so don't worry.
In your screenshot, you can see that you have a spike around 70 days ago (give or take a few days). Since your setting is for Any 60 minute period, over 90 days, and account for spikes and peaks, the alert is valid. 20 days or so from now when that spike is beyond 90 days old, they should stop.
You have told vROps that if a VM has a spike or peak, as an average over 60 minutes, in the past 90 days, which breaches 70% of the usable capacity, to consider that VM to be under stress, thus triggering the alert. The average is of no consequence. Your VM could have had a hung OS for every hour but that one in the past 90 days, and you'd still have the alert. It comes back because after you clear it, when vROps checks, this VM still meets the criteria you have set in the policies to be considered under stress.
You could change the settings of the policy ... at the VM level specifically ... to NOT account for spikes and peaks. You could also set it to Any with an elevated amount of time (90 minutes, 120 minutes, whatever) and or increase the threshold which is set in your policy at 70%. Play with the policy a bit. It really helps to learn what effects what. Make one change at a time so that you can see what impact it has, and also revert back to what it was easily. Just make sure you are doing it at the Virtual Machine level, not the cluster or datacenter, etc.
Does this help?
