The command "/osv put <new_ore> [<additional_ores>] in <stone_type>" is on the curse page, but "/osv" is not recognized as a command in the game.

Which version are you running? /osv is absolutely a command in 1.12, 1.14, and 1.16, but the put command is for 1.16 only. It's not worth backporting due to the lack of command suggestions in 1.12.

ah I see, it appears the command disappears after using /reload. After relogging its back. Then I do /reload and its gone

Was never able to reproduce this issue. I'm pretty sure it is not occurring for me and will close this issue for now. Let me know if it happens again for you and we'll try to figure out why.