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1. Where do the topics go? after a Minute I set my eyes on it and I come back again to check for that topic I won't find it
To the board where they belong to.
Altcoin related but posted on Bitcoin board goes to Altcoin Discussion and vice versa.
If it's unrelated to crypto but the post is still of good value, it usually ends up on off-topic.
If it's low-value, it goes to the trashcan.
Like what @OcTradism said, thread creator and admin/mods can move a topic.
If topic creators move their thread, you see something like this:
This topic has been moved to [BOARD].
If it's the admin/mods, you won't see a trace.