Aggregation options missing from field well columns

Hi all,

We use SSAS tabular models via a live connection to access our data.

A user has recently noticed that the option to do a simple aggregate (i.e. count) from the field well is not present in some of our models. I've compared the models where it is and isn't present and in both cases the field is a text format with "default summarization" set.

The only difference between the models is the compatibility Level which is 1400 for the model which works and 1500 for all other models. I cant find any reference to this sort of issue anywhere else.

Below are screenshots of the options I see in the 2 models from Desktop.