Well one difference between the two pictures is that the tactics are different.

There are multiple reasons that this may happen. It may be due to the difference in ninja equipment, Treasure Tools, Tactics, etc. I suggest looking at both lineup and their equipment and making sure that the ninjas are using the exact same thing in both lineups. Sometimes one lineup might be missing something the other has equipped. Each lineup is separate from the other, so the changes you make in one lineup, won't always necessarily affect the other.

~Jib

Definitely ninja equipment and treasured tools. If you switch lineup 1 to lineup 2, the best equipment always goes to your main and not your PoS1 ninja. Since main is 5 star and Pos1 ninja is 3 star, there is a difference in power. All you have to do is if you want same BP then copy where you put your ninja equipment and treasured tools.

Could be that you got older. Old age happens to us all. We are not as strong as we used to be.

In addition to what Jib said, make sure to check your summon tab as well, sometimes if you don't normally use a certain save lineup (E.g. Lineup 2), you may forget to equip one of two of your summon in the summon tab (where you can slot three different ones, preferably gold) and this means that the summon runes you equipped will also fail to add to your power

DIffer Tactic.....

Thank you guys. Now that I noticed, the problem was in the invocations, in the "contract" part. There, no invocation was selected, so the grotesque loss of power

Glad you found the reason xD