Filament stopper after 2 hour of printing

Hi all, I attached the picture shows my problem with hotend. After 1-2 hour of printing is created inside (teflon tube?) stopper inhibiting to filament continue in tube to the nozzle. All what I do is - dismount all head and clean it with 3mm drill.
I use 3mm filament 240°C ABS, I merged and its around 2,75-3mm, is it really so sensitive or there is any other problem ?.

What is the cause ? Is not real fun to clean it very often.

If this is an all metal hot end, you may consider printing at a cooler temperature. I have heard of dipping the tip of the ABS in some peanut or canola oil before loading the filament into the extruder. This lubricates the inside of the hotend. Also, be careful when boring out the hotend with the drill as this can scratch the inside of the hotend, creating grooves where cooled filament can stick to the metal. That's my two cents.

Good luck!

Ken