If you're trying out After Effects filter demos or troubleshooting problems, you might have copies of plug-ins that conflict when loading. To prevent Presets or filters (or folders of them) from loading, you can add “~” or use parentheses () on both Mac & Windows. The downside is that it's easy to forget which things are turned off when you disable a filter this way, so you may just pull filters out of the Plug-ins or Common Files folders.
This actually is in AE Help, in Remove an effect or animation preset, though it's hard to find with some keyword searches. Also, it does seem that Command+period (Mac) or ESC to stop filters loading during a launch of AE is no longer a feature.
Update: DaveS clarifies, "IIRC, option-L (¬) has always been mac-only, ~ win-only, and () works on both."