Variants inconsistently resolved in studies API with many credible sets

[jdhayhurst]

Describe the bug For studies with a large number of credible sets, the variants objects in the credible sets are sometimes resolved and sometimes not. It is inconsistent, but with more request attempts more variants are resolved, i.e. not null

Expected behaviour Each credible set, within the study credible sets should have a variant resolved.

To Reproduce Steps to reproduce the behaviour:

1. run the following and notice that some variants are not resolved.
2. repeat and notice that more variants are resolved.

   query GWASCredibleSetsQuery{
   gwasStudy(studyId: "GCST90002320") {
   studyId
   credibleSets(page: {size: 2000, index: 0}) {
     studyLocusId
     variant {
       id
       chromosome
       position
       referenceAllele
       alternateAllele
       __typename
     }
     pValueMantissa
     pValueExponent
     beta
     locus {
       is95CredibleSet
       __typename
     }
     finemappingMethod
     strongestLocus2gene {
       target {
         id
         approvedSymbol
         __typename
       }
       score
       __typename
     }
     __typename
   }
   __typename
   }
   }

Additional context Suspect a race condition, where the study and credible sets are returned before the variants themselves are finished.