Shifting print layers

I graduated to a long print time object-a cubicle coat hanger from Thingiverse. It has 85 layers and supposed to take about 2 1/2 hours. The first two attempts failed because the filament didn't feed correctly and the printer just stopped in it's tracks. I rigged up a temporary spool holder that fed the filament down from the top and it seemed to be work well. The first time, about 40 layers in, the layers shifted over about a 1/4 inch, then gradually continued to shift over more. I stopped it and tried again. This time it got about 3/4 of the way through and then started shifting again. Since it didn't happen in the same place, it wasn't the file. Any suggestions as to what is happening? My initial thought was the filament feed was tight and didn't allow the print head to move all the way over to the correct position. Is that possible? If so, I can't think of any way to make the filament feed any better.

 

I had the same issue once and I fixed securing the glass better.

 

I have the updated ABS with just the one plate. I printed another cubicle coat hanger last night, a different one but this one "only" took about 1 1/2 hours. It printed perfectly.

 

it happened with me once,
I changed my Z alignment as the Filament was barely touching the layer before and the higher it got it comes to a point where it misses the previous layer and just keeps flowing around the hot end

 

Belt is no problem,I had this problem too,I think the problem is filament,it's too tight or get stuck before it feed inside.So PC give a signal to motor,the motor just change its step angle according to G code,but it can not give enough power to extruder parts to move to right place,shift happened.