This is not the issue. This is entirely something else. We're not talking about forwarding here at all. When running PocketMine the port registers as open, when using Nukkit it does not. How can this have anything to do with SRV records forwarding when there are none.
For your problem, it's about an undone Nukkit feature called UPnP forwarding(what pocketmine have already done). And yes, we will have that done.
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If you want to know the detail for your problem, see this:
Usually for server opening home, to make server visible to internet, the route might be:
[Your computer ---Router(UPnP)-]-> Internet -[-> Client]
[Your computer ---Router(Manual Configurate)-]-> Internet -[-> Client]
[Your computer -]-> Internet -[-> Client]
but not this:
[Your computer ---Router-]-XX Internet -[-X Client(Can not find server)]
Notice that something called UPnP make it possible to bind forward automatically, but without it you could only port forward by config your router manually. To bind forward automatically, both routers and softwares should adapt UPnP.
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For SRV Forwarding, it could be:
[Your computer running many servers =]=> Internet =[=> Client(Many servers)]
For example, if you add a SRV record to DNS, that make it possible to transfer s35.example.com:19132 to h1.example.com:20991 (port changed).
