I thought I knew how to troubleshoot my printer, but I guess it that asked for troubles

Short version: when I try to extrude the filament seems to "bunch up" inside the extruder guide and then get stuck (see picture). I verified that this is not a clogged head (problem repeats with new head).
Longer version:
I was traveling for more than a month, and so the printer did not work for a while. I came back and did few single-color prints (I have a dual head) without a problem. Yesterday I tried to print with the other extruder, and the print worked fine until mid way in a ~ 1.5 hr print.
When I came to check I found the head moving but not extruding. Stopping the print I didn't manage to retract the filament. I had to disassemble the extruder and found a nice dab of PTEG filament in the middle (similar to the pic above, but much worse). After clearing that up, I reassembled everything and set another print.
The second print got stuck at a similar stage of the print. I repeated the dis-assembly/reassembly, but this time decided to clean the head with eSUN cleaning filament. The filament would extrude a bit and then start coiling inside the extruder. If I stopped this in time I could retract. Otherwise, I had again stuck filament.
I went through this several time, different speeds and different setting of the extruder tension bolt. Eventually I decided that maybe the head is clogged. I replaced it with my spare one (another v4 head), and the problem repeated itself. I verified that the spare is not clogged by manually extruding through it without a problem.
I disassembled the extruder block and cleaned it thoroughly. The problem did not go away.
Other things I tried, I verified that the extruder tip is aligned with the head tube (not sure how you call this). Problem repeats also with ABS.
Ideas?
Thanks!
-Nir