Definitely check to make sure your bore is clean. I had intermittent feed problems that degraded over time, but miraculously recovered after a brief pause in printing. Turned out to be a piece of metallic debris floating in the melt zone, never blocked it but increased back pressure until the hobbed bolt started chewing the filament. Once the filament started getting chewed in one place, it would snowball quickly and the hobbed bolt quickly lost its ability to grip and extrude the filament. Removal of the debris definitively ended that issue.