Filament may drip for whatever reasons (bad quality, too high temperature, possibly water content).

I ran into this in a five-color PETG print at max. recommended temperature. One of the colors (and, very clearly, only "green") started dripping three hours into the print. I had parked the head for tool change over an empty spot, and the resulting "blob" became very visible (usually it would be buried in the wipe tower, partly melting into it).

It's solid so it trapped the print head once it grew to Z height, causing the usual layer shift.