There's a lot of block lag in Deep Dark. The log seems to point out the issue being Recurrent Complex.

Here's the error log: https://pastebin.com/zu2VEx7x

See #155 for cascading chunk generation.

However, cascading chunk generation won't cause block lag - it will cause generation lag. As long as you don't explore, it won't show, and even so it usually isn't critical the way it is currently. I'd assume your problem lies elsewhere, or at least partially.

I just wanna add a little something, now that I have updated this mod and Extra Utils to 1.12.2 this issue no longer occurs.