Inconsistent Filament Feed

It does look like you're dragging on the bed. It is a little big strange that you could be dragging on the heated bed and then periodically push out a big blob of filament, but maybe that can happen due to the way the z-axis carriages are not constrained from being lifted up off of their bolts?

If you've had a lot of nozzle dragging, then you've probably also had some filament grinding at the hobbed bolt, which would cause feed problems as well.

After you follow Cambo's advice, I'd also take a peek at your hobbed bolt and clean out any debris (I usually use a toothbrush). Once you get a little debris in that hob, it will just get progressively worse.

Do you get periodic stringy (less than the nozzle diameter) feed through the rest of the build?

 

There is a way to determine the cause of this but the procedure is not scientific and a bit out there but sometimes you have to try the crazy along with what is sane to actually find the correct answer. Be prepared though you will have to reset bed calibrate the distance from teh bed to the nozzle tip but this should at least give you a path way to getting to the right settings. I use this process quite alot when dealing with new filaments or beds or just when things don't seem to be working other ways and it has helped me alot. Again it is not the complete solution but it gives teh direction to focus.

As the printer is printing and you see this your first instinct will be to stop and adjust something and start again but as you said you are not sure what is the cause so what do you adjust. What I do is when I see an issue with the filament path that I do not like before I stop the print I wait until the z axis is not moving or due to be moving soon and on the side closest to where it is being printed I simply turn the threaded screw a bit in either direction adn see what happens to the line of filament just a little twist like 1/16 of a revolution can have major affects on the line of filament by doing so you have now blown away any current z axis adjustments that were made previously but by noting if the filament line improves in quality and whether or not the z axis raised or lowered will tell you immediately what is happening if a small turn that raises the axis produces a better filament line then you know your z axis is too low to start with and to make sure your next adjustment takes that into consideration. Adjusting the other side to match the correct side will definitely help and may be all you need. Stop and restart and see if this goes away if not repeat.

This is also where the z stop modification comes in handy if you feel the nozzle is adjusted perfectly even across the bed then using the stop switch modification will simple raise or lower the bed height on the whole if you feel it is too low adjust the screw so it makes contact with the switch just a touch earlier than it used to the will lower the bed and you should see changes repeat this until you are happy ifyou simply get lines of filament floating on teh surface then you are probably too high and raising that screw so it contact the stop switch a touch later raises the bed and you should also see some changes again repeat this until you are happy. The draw back to the z stop method of fixing things is that you need to stop the print re home everything and restart the print each time to see if the change is the right amount.

The good thing is it pretty much always works eventually.

This is only if the issue is related to the height of the bed and not if it is due to other reasons like a clogged nozzle or stuck filament.

Enjoy your printer and I hope this helps

A caveat this kind of and adjustment is really for people who are used to their printers and how it works. These adjustments do work as I have used both types successfully several times but it can get a bit confusing so take it slow and ask questions. I actually used the first method today when I started using Nylon (new for me) on a newly adjusted bed and found out my nozzle was a bit too close I turned the rod the axis on one side raised, the filament line got better. I stopped the print adjusted the other side to match as closely as possible and retried and the second print attempt was fine.