Can't track mutation from ORF1ab

I tried to query several mutations in ORF1ab, e.g. ORF1ab:P4715L, but the output was empty in outbreak.info webserver as well as in the R API. However, mutations from other proteins had data on the output (S,N,E, ORF7a, etc). Any idea to solve this problem? Or Am I doing something wrong? 