Unisphere 360 - certificate error when adding Unisphere instances

As the title describes, we have installed Unisphere 360 and are now in the process of adding Unisphere instances to it so we can get a single view of our storage estate. The versions of Unisphere are 8.4 and compatible with Unisphere 360. It will allow us to add some instances and in some cases allows us to "add security exception". However there are a number of Unisphere instances where it says communication error at "http://*** " failed due to certificate error. Anyone else come across this or recommend a way to fix this please? With these instances that fail, the "add security exception" option is greyed out.