Our mod log will show all federated mod actions, not just actions by lemm.ee mods and admins. So if any other instance is generating a ton of actions, it will also be visible from our mod log. In fact I don’t think there has been any increase recently in lemm.ee mod actions at all.
The mod log does not actually get cleared, there is simply a UI issue in Lemmy which makes it a bit hard to view the mod log chronologically. The UI makes it appear as if the mod log is one single list of actions, while in fact it’s different lists combined together (one list per each action type). You will notice some really old actions even on the first page of the mod log, this makes it seem as if there is a “missing period” in the actions, while in fact you are actually just seeing the first page for each different action type. If you navigate to subsequent pages, you will find all the “missing” actions there.
In practical terms, it’s not really possible to clear the mod log at all, thanks to federation. Even if one instance will delete their local mod log records, those records would still be visible in other instances which they previously federated out to.