Easiest and cheapest solution to rule out would be replace the gas cap. Sometimes it goes bad and doesnt seal.

 

My policy. Before you load the parts cannon, if lacking solid evidence always go with the simplest and cheapest solutions first.

In this case, failed gas caps are fairly common. It is also amazingly common for the gas cap to not be installed properly. Turn it till it clicks.

 

2015 Q50
My engine light has been on for years (it will be off for a day or two then re-emerge) and I have been told it due to a faulty vacuum pressure sensor. No impact or performance and a whole day required to remove and replace - advised that its not worth it.
Coincidently my gas cap warning pops up infrequently (once a year) ( reset and it goes away). I was advised that they are a related issue.

By advised I am referring to professional service technician.

Any thoughts on how to solve the problem once and for all?

It would be helpful to know the specific DTC your tech found but if it is indeed the EVAP control system pressure sensor, you can buy a new one on eBay for about $30. It is located on the EVAP canister (#1 in the diagram below):

The EVAP canister is located behind the rear bumper fascia on the passenger side. I don't see how it would take a whole day to remove the EVAP canister as there is only one bolt to release it and the rear bumper fascia doesn't need to be removed to do so. Your EVAP canister should be checked to see if it is full of water also. Your gas cap warning is due to the same issue.

 

my last nissan had the common gas gap deal too which I replaced once, but it usually boiled down to EVAP, basically you could buy sometime w the gas cap or it wouldn't fix it and end up going back to the root cause, EVAP.