Nope...there might be different reasons behind this. Just to list the few I come up with in a few seconds:

1.) Damage is heavily dependant on the affinity you are attacking. You might get weak hits on certain affinities

2.) If you are using Geomancer, he is more effective against non-void bosses as they attack twice and get hit back

3.) my damage range is also dependant on rng and shifts for several millions. It could be a series of bad luck.

4.) even improving a champ sometimes results in lesser damage as they can get *out of sync*. As you mentioned not to have changed anything, I guess this is not the case.

I'm doing it on void - so no afinity to worry about, I don't use Geo on void and I haven't changed anything about my team, guess it's just a bad day :(

Did you drop to a lower arena rank?

Sometimes it is just rng. I myself experience 5-6 million difference in my bat eater comp. 

Other factors are crit rate. If your champions do not have 100% crit rate, then expect that there will be days that your cb team will go below your average damage. 

Gear sets like relentless, reflex, on lucky days, it will proc more. 

Masteries, like reduce cooldown, warmaster, giant slayer and counter attack, these are dependent on rng which can also affect your overall damage if they did not proc like in most of your runs. 

There is not only rng about critchance on your side of the fight. I guess much more influence has the critchance of the CB himself. He has a low critchance of 15%. If it procs he may take out a champ of your team much earlier than usual.

Reduce critchance is an underrated debuff vs. CB. If that debuff is active, with his low critchance he can never land a critical hit.

Hi forrestleigh! The guys pointed out the main reasons why the performance of your team might differ time after time. However, just to make things crystal-clear and to prevent misleading assumptions there is a statement from the official representative of the company - no changes have been made to the balance, stats, or mechanics of the Clan Boss. It's absolutely the same beast you've encountered so far.

Thanks guys