Dimension Index Question

Hi were are having an odd problem with loading performance of a certain cube in our system where it is taking four times longer than the previous average. Looking into the index creation job we can see that the job is not actually creating dimension indexes apart from the request ID dimension.

Historically it did used to created the dimension indexes but over the last two days this has not been the case.

Under what circumstances would you expect this to occur?

We are on 7.2 Revision 5

PS Not all of our dimensions are line items