I guess this Raid was during Partly Cloudy weather. There are few things that game analyze during auto selection. It choosen Ttars because of their durabilitu VS Mewtwo and it choosen Rock Ttars because of current weather, completely ignoring boss weakness.
I have similar situation on most gyms when against Blissey and Chansey game chooses Aggrons because of their Steel Typing which is good against Dazzling Gleam.
Auto select counters to mewtwo?!
In the recent mewtwo raid, my fleet of tyranitars were auto selected. Finally, I found that mewtwo was of psychic, but only my ttars of stone edge were selected (however I got more crunch ttars of same level than SE ones).
Just curious why it happened...
Answers
Actually the game prefers SE Tyranitar to C Tyranitar against Psychic targets even when neither type is boosted. Have lots of experience of this from last year raiding Alakazams. It seems to be comparing the movesets based on raw DPS and because SE is a stupidly fast move, it has crazy DPS for that short move duration, more than Crunch has even with supereffectiveness factored in.
It's not a bug, it's just that the autoselect algorithm isn't very good at what it's supposed to be doing. It values survivability too much and doesn't know how to calculate real DPS. Other examples are Hu Dragonite always getting picked over OR Dragonite and CC Machamp always getting picked over DP Machamp.
I think it must take the power of the bar rather than overall damage, so the power of a 1 bar charge move wins out over 2 & 3 bar moves everytime. Silly really as we all know multiple bar moves are better in gyms & in raids. I pretty much ignore auto select unless raiding in large groups where it really doesn't matter.
Per the comments above - I learned in recent months to never count on the auto-selection (because Aggron's going to show up often), unless maybe you're near the end of a raid and just need a fast 2nd-string team.
Get yourself an app like Poke Genie that can look at your collection and help you pick the best counters. I find it's often dramatically different.
It definately prefers SE > Crunch like all 1 bar moves over 2/3
Worse though it takes it to the extreme of evening prefering Smack Down SE > Bite/Crunch
I wish we could have a little control over the autoselector. Like a 2nd Star of Left side that is blue on/off toggle "Eligible for Autoselector" and it forced the auto to pick only from that selection.\
Probably partly cloudy, the same thing happened when I did my 3 mewtwo raids, it picked my maxed out B/C one, and then the rest were all high level SD/SE ones because of partly cloudy weather. The recommended counter's are determined in a pretty dumb way that most of the time doesnt give you the best options, it goes for most resistance to the charge move and if you have any pokemon with weather boost (ie, picking an aggron agaisnt hyperbeam because its resistance to normal is greater than tyrantiar). Sometimes it gets it right, others it doesnt (mostly it gets it wrong)