How many saves do you need to make for multiple umber hulks?

[holywhippet]

In the last session my group had we ran into a trio of umber hulks. I noticed our DM was asking us to make single saving throws even if multiple umber hulks were in range. I thought that, by RAW, you'd make one saving throw for each umber hulk who'd eyes you can see.

[DeTess]

There's a general rule that multiple simultaneous effects (such as a paladin's aura) with the same name don't overlap. I suppose the DM applied that rule here as well.