Agree with @bitwolf, that looks like “heat creep” to me – typically caused by the little “5v micro blower fan” not running, or running too slowly. It’s a common failure item on that extruder (I’ve replaced mine twice). Check that the fan is running. Even if it is running, with age they can slow down or collect dirt on the vanes such that they just don’t move enough air. Pretty cheap and easy to replace if needed. Lulzbot normally carries them (not sure if they’re selling parts right now though), as does the itworks3d.com site.