I think it is rather the exception than the rule that a team which is performing bad in the domestic league is one of the strongest teams in the Champions League. Yes I know that now some people will come up with examples, like Sevilla and how they won the Europa League last season when they were so bad in La Liga. But where is Sevilla now? They finished their Champions League group with 2 points out of 6 games and got destroyed in almost every game. There is a correlation between the overall performance of a team in the league and the other competitions, but yes there are exceptions of course.
Some teams have poor performance in domestic league but success with quit well performance in Champion League, difference with Sevilla performance in this season not only poor in La Liga but also failed and finish on bottom standings in Champion League group phase. But another teams Napoli have quit well performance in Champion League and success qualify to knock out round although with 2nd standings finish position but they have poor and inconsistency performance in domestic league.
I think domestic league and Champion League have difference atmosphere and some teams focus with quit well performance in Champion League but they have poor performance when playing in domestic league.
I have to agree with you that local league and champions league have different atmosphere. The issue of a team performing well in the Champions League but in awful condition in local league and vice versa did not start today. We have seen teams exhibit same thing even the big clubs like Manchester city and Real Madrid.
Take Real Madrid for instance, I am witness to when they were in a poor form in the laliga but in that same season, they were able to win the champions league. Again, present Manchester City is not in a good form in the English Premier League but they have a flawless record in the English Premier League.