It is a Retention SIM offer (signified by the R) which falls outside of the usual tariff definitions.
It may be that you've got Unlimited Data and EU Roaming agreed on there in line with what you would get on an Essentials Plus plan, but as it is not exactly an Essentials Plus tariff and is a promotion/retention offer it would likely not be eligible for the additional features of a normal Essentials Plus tariff.
The Unlimited Watch Data feature would check the tariff code, which in this case wouldn't match automatically for discounting as it isn't an Essentials Plus tariff but a Retentions one with EU Roaming included.
