If you're aiming for entirely hollow, that's your problem. Howabout something like Lightning infill that's designed to be almost not there and just provide minimum support?
The tail, I reckon you're right there with the minimum layer time or not enough cooling - the heat of the nozzle has melted previous layers. Perversely, it could be minimum layer time that's CAUSING the problem as one of the options (if I remember correctly) is rather than print layer, wait, print next layer, it will just slow down the extrude so that it takes at least the minium time to do the layer. That slow movement is what would be causing the re-melting. Worth a check of the timelapse that you're bound to have turned off on the one time it would be useful!
You might be on the right track with the separate item to soak up layer time but the downside would be that you'll get stringing to/from it instead....unless you've really nailed it with those retraction tweaks.