Automatic topic split?

I have a topic that gets lot of responses and it split at 990, locked the original and started another.
I tried to unlock and merge the two, but it won't work.

Is there a default that I can change?

hello

you cannot remove it, this is a limit that Forumotions has
Messages in a subject: 990 messages (once the limit reached, the subject is locked and splitted)

Is this also the case with paid versions?

No matter what version you have, you can not disable it