Typically only one layer of underlayment is allowed, if attached that is it. But check with the manufacturer but expect them to say with an additional underlayment, no warranty.

That would seem to be the answer . Is this in a condo where noise has to be very controlled ?

It's not a condo requirement and I am getting the Gaia Red series - sole (8mm) . So manufacturer says don't use additional underlayment.  I currently face 2 options 

Option 1 - Have the rubber underlayment but risk warranty.Also doesn't extra 6mm of rubber underlayment help with added sound proofing and heat insulation 

Option 2 - If we remove the underlayment and install LVP directly on the subfloor, there would be a drop in level because the rubber underlayment is 6mm thick ( this would cause gaps at the door trims ). So the workaround would be to install quarter inch plywood and then install LVP . But this is giving an additional cost of $2.3K . 

The dilemma is whether to spend 2.3k now and have the warranty or install LVP on top of rubber underlayment and risk warranty. Does installation of Lvp on top of rubber underlayment cause any issues

No offense..............but why would you risk warranty and quality of install for 2300.00 dollars ? Over five years? This is 460.00 per year to have a 20 yr floor with reasonable care.

What to do you spend on take out pizza in a year? On a daily drive through coffee?

" Does installation of Lvp on top of rubber underlayment cause any issues "

Two layers of insulation very well may cause the click locks to break since this will basically be a floating floor.

Click flooring is a tricky thing to begin with making sure the subfloor in totally even so I agree why void the warranty at all.My advice always is do it right to begin with and in your case that meas the rubber removed and eithe live with the bigger gap under doors or install the new sub floor . IMO beats the heck out of the flooring shifting and popping out of the click

Thanks everyone for your input. I have decided to go ahead with rubber underlayment removal and thereby keepibg the warranty

Take good pictures every step of install beginning to end. Lay a long level on that floor and snap that too. Warranties are..........very difficult to enforce in reality. Impossible, without documentation of ever step of process, should you need to enforce . All products used included.