This seems to be since the latest (18.4) update to After Effects, but I sometimes can't click and drag keyframes along the timeline. It's not all keyframes, just some and there seems to be no pattern to it.
I can select the keyframes fine, but if I try to shift them left and right and they won't budge. Other layers - even duplicates of that layer - work fine, but this one layer just won't move. It's not even linked to a specific layer; sometimes it does and sometimes it doesn't on just about any layer as far as I can see. If, however, I select the keyframes that won't move, and then select ones on a different layer, then I can shift them all together, so it doesn't seem like some kind of setting that I've applied to lock the keyframes in place.
Could this possibly be an update glitch? I can't reinstall the whole thing right now as I'm mid-project and it's not major enough to warrant a full reinstall, but I wanted to check if anyone else has been experiencing this.
When you have that problem again, select the problem layer, press 'uu' to reveal all modified properties, make sure both the modes and switches columns are visible by selecting the first two icons at the bottom left corner of the timeline, take a screenshot of the entire UI and embed it so we can see what you are dealing with.
* The "Drag & Drop here..." area is buggy and should not be used to share images. Please use the toolbar or just drag your images to the reply field. If you can not see your image before you hit post it's a pain for us to see it.