Russian players have been reporting 13vs13 battles and it seems to be happening quite often. Wargaming is already investigating the issue as this wasn’t an intentional change.
FromKONI: How did it make sense to change the format of 15vs15, making it 13 vs 13 did it get anything with this?
unball: We are already looking into why 13vs13 battles are happening.
If you get any 13vs13 battles, please do let me know in the comments section, but this should be fixed quickly.
I didn’t get any reports yet from EU or NA Servers that this is happening, so it could be an isolated issue for the Russian Server, but this isn’t confirmed yet.
Source: World of Tanks Russian Forum
Thank you for everyone who replied here and on Facebook. It seems it happening on all Servers, and NA had the issue since 9.18 was released but it was overlooked because everyone thought it could be related to low population issues.
Turns out it’s not and it’s happening across all servers and tiers. I had confirmation from Ph3lan that Wargaming is looking into this issue, so we should have a fix soon.