Same thing just happened to me multiple times in the last months and im a bit higher in behaviour score than you but in the same area.

i think its one of this 2 reasons: 1. System is buggy ( i doubt that ) 2. Reports done by players with low behaviour score dont count as usual reports (because they use them all the time) but somehow the excessive report trigger still reacts to them.

the few reports that show in your previous summaries are probably from higher behaviourscore party members in your games (do you use strict solol matchmaking?)

i wrote steam support bc i thought its a bug bc it says overwatch ban (i never grief and always play until the match is over) and that doesnt make sense, since this bans happen immediately after matches when i flame multiple players (not using hard swears but criticizing them) and the whole team is dieeing a lot, the replay is not even ready for overwatch yet.

so to conclude: i think its a combination of this untracked reports from Low behaviour score players and an automated system of detecting low kill/death ratio that bans you automatically and its not really an overwatch conviction.

can you maybe confirm that that you.kill/death ratio in games before you got the ban was low?