It could be a bug.

If it's not a bug, other reasons: If those 20 sats came from someone whom everyone trusts 2-3x more than you, it'd cost you >10k sats to outlaw it on your own. If the difference is even higher, it'd cost you >100k.

Also you're all gaining or losing trust everyday depending on what you're upzapping and downzapping. If you had an easier time outlawing before, it might be that you lost some trust.