I have the same issue, iPad 6th gen with iOS 12.3.1.

I have attached screenshots of what’s happening

bump!

im getting same issue exactly the same, only uses 3 of the 4 champs yet shows in multi window at end of each battle 4 champs were selected

This is a prime example of the 1st Rule of Coding. "If it isn't broke yet it will be at the next update."

This is a widespread issue and is affecting multiple os's.

 It leaves 2 man teams alone but drops champs from 3 and 4 man teams.

Device: iPhone 6S

OS: iOS 12.3.1

WTR (way to reproduce an issue):

Step 1: Go to any campaign level (I have only tested normal and brutal difficulties)

Step 2: Select a mix of max-level champions (for their rank i.e. level 30 3-star champions or level 40 4-star champions) and non-max champions 

Step 3: Launch a multi-battle with any settings

Description:

I confirm that multi-battle is broken. Wasted a bunch of multi-battles yesterday and today trying to figure out what was going wrong. Looks like every time I put in a max level champion, it gets left out of the actual fights but then pops back in at the end when the summary is provided. See following screenshots.

Screenshot 1: selecting four characters, one of which is a maxed 4 star.

Screenshot 2: configuring my multi-battle settings

Screenshot 3: battle begins but my max level is missing!?

Screenshot 4: missing character still appears in the multi-battle results summary

Like many, I mainly use multi-battle to level up three food characters with one maxed-out champ. If my maxed-out champ, who is carrying the food, gets omitted every time then multi-battle becomes useless to me. Please fix this ASAP.

I use a Galaxy S7. I experienced this today while grinding for silver, so I had four max level champions running 12.6 on Brutal. Like others, I left my phobe alone while going about other things, and came back to only my leader there, dying on battle 15. The rest of the team showed up in the summary. :/

Same here cant use 2 max lvl champs since last update