Created attachment 32800 [details]
Reproduction test plan

I found strange issue with using Counter element under Random or Interleave controller. The strangeness is that it can be fixed just by wrapping the sampler into Simple Controller.

See the attached test plan, it contains 2 thread groups. Fail thread group shows that counter variable produces not sequential values, although it is attached to a sampler. Surprisingly, Pass thread group shows that just wrapping the sampler into Simple controller do produce desired sequential integer values.

I failed to find obvious reasons for such behavior while reading through source code. I expect Counter to produce sequential values even without being wrapped into Simple Controller, at it feels natural by attaching it to particular scope.