Recurring Problem - TPS leaks? (tick per second)

Note: It's a TPS leak not Mem leak, Memory stays constant (90% or so) throughout

Are there any plugins that are known to cause 'TPS leaks', where the server's TPS drops from 20 to 15 to 5 and then back to 20 again after 10 minutes or so?

My server was running fine 3 weeks ago, I updated plugins to R4 and then I started have MAJOR TPS leaks that would crash my server. So I installed NoLagg as a bandaid fix and it worked. Now, 3 weeks later, I'm having the same problem but with NoLagg installed. I haven't changed anything on my server and all plugins I DID add I removed (but it still happens). I've tried removing all entities to no avail.

The problem isn't that the TPS dropped for a minute or two and then comes back up, instead the ticks stay at around 9 for most of the time then drops to 5 then hovers at 20 for a while. Basically, my server is running at 5-10TPS half the time. (Before any of these problems my server ran at 20TPS almost 100% of the time)

I'll post a full plugin list later, just wondering if anybody was aware of this problem and could point me in the right direction.