We have an announcement rather than a micropatch which must mean a fix hasn’t been found yet. From Wargaming support:
We have become aware that in some very rare cases the battles are not loading. This is causing the battle to not be played.
It has also been noted that any player is affected is not able to log into the game for the full duration of the battle (15 minutes)
We are working very hard to resolve this issue and we are sorry for any inconvenience this may cause.
The Customer Support Team