Our server is having an interesting issue with this mod installed: along with the already reported cascading lag issues that have already been reported, we've noticed that having this mod installed impacts the time between each tick heavily.

With one person on, without this mod, each tick has a delay of about 15ms, however, with the same player on it sits around 48ms. This is even when the player is idle, not generating chunks. While this can be mitigated by using a mod to pregen the world with RC installed and then remove the world, this process can take weeks especially with post-processing which is required for RC stuff to spawn.

We are running RC complex 1.4.6, though it doesn't look like the changelog impact optimization. We are also running forge build 2584, with a Biomes o' Plenty v2310.

Can confirm this is still an issue with the latest version; my worlds are getting lag up to 6000 ms, removing RC does drastically lower the lag. If you leave a server/client-server up for long enough, the lag gets especially worse as time goes along. This is a memory leak issue as well, not just TPS.

TPS drops get especially bad after the server previously generated some chunks, but it remains bad even when players aren't rapidly loading chunks. Seems like RC's world generation is running constantly in previously-loaded chunks.

Not in lightweight mode

I can't really imagine Recurrent Complex affecting tick time. Chunk generation time - yes, if a lot is generated, although after the first bit of playing chunks should generate slow enough that it shouldn't be a big problem. I'm guessing most of your lag is the chunk generation MC does even when you're idle, and your lag is caused by a lot of mods causing cascading chunk generation together.

Currently, our set up is on a VPS however, we've noticed that when idle with Recurrent Complex the lag is higher. That being said, I hadn't really stopped and thought about it being a mod conflict. Strangely, this issue only happens when RC is set up to only run server side.

You mean in lightweight mode? That's also hard to imagine, but then again I haven't really checked that side extensively...
Can you check if it happens for you with just ReC installed?

It doesn't seem to. Hard to tell tho.