Could be a bug, it does seem suspicious that it seems a new TE is created every tick. Or it could be a legitimate memory leak.
I made a hprof memory dump on the server and will check it out, I couldn't get jstatd working but might try a JMX connection - it only takes a couple hours before it starts to build up. I just need a way to track/catch the allocations, Warmroast and Opis only care about CPU (which I may be able to catch once it reaches that ~2 million account again but I think the lag I was getting was actually from GC working in overdrive - so again the CPU profiling of warmroast and opis wouldn't be able to help with that).
EDIT: Just looked at the hprof dump - confirmed, there is indeed a ridiculously large number of thaumcraft.common.tiles.TileNode instances. Unless it's specific to my mod collection (don't see how), Thaumcraft 4 has a serious memory leak. It's creating new TE's when it has no need to do so.
Is the author still around? Maybe I can ask them to peek at the code.... Or maybe I can decompile, not that I'd be able to recompile it successfully...
Well, it is definitely specific to your mod collection. As I play TC 18.104.22.168 all the time in packs like Simply Magic and this problem does not occur.
My previous experience with this was a FTB pack - Direwolf20 for 1.7.10. And between Twilight Forest (strange wroldgen of "ruins" but full of end game ME blocks) and Factorization (its extra dimensional system to make its big robots did strange things) I did, occasionally, see millions of things. But as I said I never tracked them down.
TC4 does have a memory leak on servers - related to the aspect orbs it drops. Unstable nodes that are in loaded chunks drop aspect orbs, but if the chunk is not processing ticks (has an unloaded chunk within 2 chunks, spawn chunks, etc) the aspect orbs do not despawn, causing 10's of thousands of entities to build up and cause lag. (Unstable orbs can generate in the factorization dimension and as FZ only partially loads those chunks, if a player wanders past a colossus this kicks off the process in that dimension.