Why do addons work only sometimes?

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    My addons work randomly

    They sometimes work but many times they dont

    If they work once,they keep working till the server stops

    I am using oneplayer sleep addon and fastminer

    i do not think the problem is with the addon

    Because i have uploaded the same .mcpack file that i used for singleplayer and it works completely fine

    And even if it was addon's fault then why would it even work, it can work sometimes but not always.