stackoverflow usually has pretty good answers.. ..but this community is more active and has users that know pocketmine.. as in exp.
if the issues are about PHP syntax and plain/complex php stuff then post on Stackoverflow if the issues are about PM-MP development (and plugins) then post on Pocketmine Forums
Yeah, usually StackOverflow is good for general knowledge questions, but for questions about a specific software (like PMMP) it's best to use their provided forums/help centre.
This legendary PocketMine developer + plugin developer seems to be (the only one) active on the StackOverflow pocketmine tag. At least he has ask-and-self-answered a few questions related to it.
i don't think it will happen mods here don't lock threads once things is sloved (like IM which i absuletly hates), they only lock it if things gone too bad {via observation}