Perhaps the trash filewalker removed the expired data from the trash and the used-space-filewalker finally updated databases to reflect the actual used space, and the TTL based data has been removed (it is deleted by nodes without using GC or the trash), also the garbage collector finally moved detected garbage to the trash.
You may check all of that:
or for Windows:
Your change in the router is not related to this, unless you also unblocked connections from the satellites and customers to your node.
If you have some “smart” protection feature or “DDoS protection” on your router - I would recommend to disable these features.
The only coincidence here is a timing in my opinion, because almost all filewalkers are time based.