Effects apply slowly, but I want immediate


I am just starting to use Audacity. I am trying to apply a Tube Amp effect to a recorded guitar track, to create a distorted sound. When I apply the effect, the signal remains dry in the beginning of the track, and then gradually increases towards a more affected signal. I want to have the effect working equally along the whole track, but I don’t know how.

I attached a screenshot. The upper track is the unaffected track, the lower one is with the effect applied. you can clearly see that the amplification gradually increases.

Any tips?

I presume the tube amp is a plug-in because Audacity does not ship with a tube amp.
Perhaps you could add some silence to the start of the track (Click on the track where you want to insert the silence, then “Generate menu > Silence”), then apply the tube effect, then delete the added silence.