If you get grease into your garbage disposal grinder, I’ve heard you should use cold water to get it to congeal so the grinder can break it up and it will continue flowing once it’s in the drain. If you use warm water, it might flow, but only long enough to then solidify on your drainpipes.

Maybe something similar is happening on the hard drive: sticky is too viscous to flow at full speed, but solid just breaks apart and dances around on the platters while the heads can make contact with the magnetic media.