Spatial Index warning from Spatial Query

I’m trying a spatial query using QGIS version 3.10 using a buffer layer and a set of species records. I wish to know how many species records fall within the buffer. When I perform the spatial query by going to Vector>Research Tools>Select by Location and fill in the input layer as species records, type as intersect and comparing features to buffer layer I get the following warning: ‘no spatial index for input layer, performance will be severely degraded’.

I’ve added a spatial index to the layer and still get the same warning occurs.

Does anyone know what causes the initial warning?

Interestingly when I try on another laptop of the same spec with the same layers it works fine.

Is there something in the settings that could resolve this issue?