In SERVER-126823 the fixedBucketing value is set to true if the fixedBucketing feature flag is enabled on all viewless timeseries collections that are created. This is wrong because the default timeseries options are not fixed bucketing. Additionally, even if the default is fixed bucketing the user can always pass in granularity, which would make the collection not have fixed buckets.

Instead of always setting fixedBucketing to true for new viewless timeseries collections, we should only set fixedBucketing to true when fixed bucketing applies (bucketMaxSpanSeconds and bucketRoundingSeconds are set by the user and equal to each other)

[Update] there is no bug. The fixed bucketing flag was implemented to mean that granularity was never changed since TS creation. For the query optimizations we also check that bucketRoundingSeconds==bucketMaxSpanSeconds so the code is correct. We might consider renaming fixed bucketing in the query code to clarify that the bucket boundaries must be aligned, but that will be done in a different ticket.