Have not tested this on single player, have only used this mod on our server. Everything is fine until we get near a nether portal. the console goes crazy with netty errors causing server lag. i have turned on advanced reporting and below is a snip of the error.

Full Error: https://pastebin.com/CsDbk23y

BTW this is what i get on the client side around the same time as the netty error on the server:

[20:46:01] [Client thread/WARN]: Shader betterportals:render_portalcould not find sampler named depthSampler in the specified shader program.
[20:46:01] [Client thread/INFO]: [biomesoplenty.common.world.BiomeProviderBOPHell:<init>:32]: settings for hell world: 
[20:46:01] [Client thread/INFO]: Creating Nether SeasonInfo for dimension the_nether
[20:46:01] [Client thread/INFO]: Setting weather renderer for dimension [the_nether]
[20:46:02] [Client thread/WARN]: Dropping packet net.minecraft.network.play.client.CPacketConfirmTeleport@6676e9c4
[20:46:02] [Client thread/WARN]: Dropping packet net.minecraft.network.play.client.CPacketPlayer$PositionRotation@be8fd2a
[20:53:16] [Client thread/INFO]: [biomesoplenty.common.world.BiomeProviderBOPHell:<init>:32]: settings for hell world: 
[20:53:16] [Client thread/INFO]: Creating Nether SeasonInfo for dimension the_nether
[20:53:16] [Client thread/INFO]: Setting weather renderer for dimension [the_nether]```

The lag seems to have greatly reduced. i have not tried single player yet but below are the full logs for both the server and client. Netty error still occurs when first approaching the portal. ill test single player later.
Server debug Log: https://www.dropbox.com/s/1ixu803rkjxnkkj/debug.log?dl=0
Server copy from terminal of netty details: https://www.dropbox.com/s/ddq0mo2uz17wv00/Console.txt?dl=0
Client Latest: https://www.dropbox.com/s/ezn0pjo8dnvlpvl/latest.log?dl=0

I'm unable to reproduce the issue myself (tbh I wouldn't have been surprised if it was just BP on a dedicated server, it's been probably over a month since I last tried that). Instead it's probably related to one of your mods. Could you please

1. check if it happens in SP (debugging SP is way easier for me)
2. remove as many third-party mods as possible until you're left with only one (or none)
3. then post the full log

Please try using BP 0.2.x, lots of stuff has changed internally since 0.1.
If that makes no differences, 1. and 2. from above still apply.

Also, FYI editing issues on GitHub does not notify other people. When you've got new stuff be sure to post a new comment.

Fixed the netty issue. When adding this mod to our server, we had lots of issues getting the server stable but found that it continued to get worse and worse. Luckily the server was fairly new, we took a vote and started a new world. Now everything is working flawlessly :) you can close this, delete this or whatever. Thank you so much for trying to help :) maybe this could still be beneficial info for you.

I'm aware of some performance issues which (although they should theoretically exist in SP as well) appear on dedicated servers: #150
Those are fixed in-dev and will be in 0.2.4 once I find the time to release it (if you know how, you can also build the mod from source to get them early).