Filament jam on the tube entrance
Something is stopping the filament from going down the tube 30 to 40 min. after you start printing.  You are correct that this doesn't sound like a clogged nozzle.  It could be deformed filament, but the closeness of the timing after the start sounds like heat creep.  Other possibilities are also listed at the linked stackexchange article.
Note: with heat creep the filament will not jam in the tube.  It will jam just above the nozzle on a Bowden tube extruder; thus the filament stops going down the tube.  The tube entrance is probably the largest location the tube can kink, although not very large.
What are ways to avoid heat creep?