Duplicate: Flickering Tick Chart / Volume or Tick Bar

[Milosz]

You will probably find a solution here:

Amibroker open and close for previous bars keep changing

Tick counting starts on day boundary. If PAST ticks for current day are added by data source (for example during backfill) then number of ticks changes and it will affect N-tick bars, until source stops adding past ticks for current day (i.e. when backfill is complete). So for stable N-tick chart you have to have at least one COMPLETE day worth of data.