Thaumcraft-1.7.10-4.2.3.5
forge-1.7.10-10.13.4.1614

So long as client is connected to server and chunks containing nodes are loaded/unloaded, Thaumcraft accumulate orphaned tile-entities client-side.
It is causing dramatic FPS drop over time.
Disconnecting and reconnecting to server is enough to recover normal FPS because it purge client-side orphaned tiles-entities.
@Azanor I understand Thaumcraft 4 is replaced by Thaumcraft 5 on MC 1.8.x, but lots of packs are still relying on 1.7.10 as lots of significant tech mods are skipping 18 altogether.
Could you please look a bit closer to your older code and at least add some orphan entity clean-up routine if you cannot fix the root cause?