On campaign, difficulty changes and I didn't change it

Hi, I was playing alone insane campaign act 3 chapter 2 (Rocket plan). I was on insane before the part when you fight on the lift against many swarms and 1 dropshot Scion with a Bastion. After that I didn’t know when the difficulty changed, but after 3 checkpoints I check that the difficulty said Intermediate on pause screen. Hopefully I was streaming so I can saw that after 1 checkpoint I paused and then is intermediate on pause screen.

Someone has/had this problem? I don’t want to complete that part again… And I don’t want to start checking my pause screen everytime that I reach a new checkpoint.

Edit: I started my new campaign on insane, I never changed difficulties since I started it because I want to complete it alone and that’s why I’m streaming because maybe the videos can be a guide for players who want to play it alone