Could this be a bug, or am I missing something?

[wind igloo]

I used to complete this content with this same team without any issues. It seems that Monelisse's Teardrop effect isn't activating correctly.

[river path]

At minute 0:57 you can see that Flora gets the immunity but it is cleansed by the boss attack instantly (occurring at the same time)
Erriches does get activated normally.
Felicity gets cleansed instantly as well.
Garius does get the immunity buff as well but dies to some attacks shortly after

As far as I see it everything works as described

[plain gate]

Hello Traveler, I am glad to serve you. Please wait for a while. I'm going to check your question.

[wind igloo]

But did you notice that the immortality icon that should last 3 seconds doesn't appear? I set the speed to x1 to make it more obvious. This wasn't happening before. 🥹

[plain gate]

Dear Traveler,

From the video you provided, it appears that the buff effect from the equipment was removed by the Boss’s skill at the moment it took effect. We recommend turning off real-time combat and checking the icon display on Flora.

I hope my reply can help you. If you have any other questions or suggestions afterwards, please feel free to contact us again. Have a great time.

[wind igloo]

Thank you very much! I couldn't see the icon in the flora, but I'll try to check out the boss's ability to negate the immortality granted by equipment.

[river path]

Sometimes when buffs are cleansed to fast or are just too short they don't show up in the window you have open.
Everything in the background shows and works as intended as Flora has shown you with the screenshot. My above answer was referring to the same thing 🙂

[quiet stag]

So basically that gear type is not worth having? (Seeing as it appears to be useless)

[river path]

It is useful. But at the same time something dispels a buff (here immortality) the buff will not work anymore.
In this case the enemy dispelled a buff and deals dmg so everything works as intended

[wind igloo]

I believe it happened so fast that I couldn't see the immortality icon. It probably activated immortality, and at the same time the boss's ability removed the buff and dealt damage.