Autoblock messages, as shown on Special:AutoblockList, take the form:
Autoblocked because your IP address has been recently used by [[User:$1|$1]. The reason given for $1's block is: "$2"
The message has been customised on the English Wikipedia to:
Autoblocked because your IP address has been recently used by "[[User:$1|$1]]". The reason given for $1's block is: "'''$2'''".
which doesn't look like it should break anything.
However, as seen in the attached screenshot, the message is truncated for a block on user "எஸ். பி. கிருஷ்ணமூர்த்தி" (might be Unicode-related?) It's not a rendering issue; the rest of the sentence is actually missing from the HTML.
I would expect to see the full message, including the reason for the original block.
The above user's name appears to be handled correctly elsewhere, for example on their user page, logs and contributions.