Real Madrid performed poorly in La Liga last season but played well in the Champions League, losing to the reigning champions in the semi-finals. So it may happen that this season they may do well in La Liga but poorly in the Champions League. We have to wait for the group stage and see how they perform.
The majority of these teams are able to recreate their domestic league performance in the Champions League. But, as far as I can tell, everything still relies on the team they face in the Champions League. The manner a team plays against a weaker team in the local league should not be replicated in the champions league, where top teams from various leagues compete. This, I believe, is what is developing into what people see today, in which some teams perform well in the domestic league but perform poorly in the Champions League.
In some instances, the reversal is the case, and this may be related to where the team's goal is; for example, they may desire to win the Champions League and place more emphasis on attaining success there than in their home league. No one can predict the outcome of each team's Champions League matches until the competition begins and we see how each team performs.