The left paw was the problem, today.  Yesterday's right paw issue was caused by a rock, not a shoelace end.  Today's issue was chafing from the left heel being too tight & compression of the foam.  The foam compressed a lot more than normal shoe foam, under the forefoot.  It was pretty rough, near the end.  Not sure how barefoot runners do it.  Compression was a bigger problem than loss of material.

Made the toe strap loop back to the heel, to eliminate any knot issues.  Used a bowline to tie the toe end & a half hitch to tie the heel end.  Half hitches may be enough for everything.  There's definitely a need to adjust, as chafing flares up & the toe flap starts flopping.  Would make the lace only go one pass around the heel & use separate laces for the toes & heel.  Having a bunch of knots where a shoelace would normally be tied hasn't been a problem.

Plastic squares succeeded in protecting the foam from loops.

Well & truly crushed in only 17 miles.  Would say they did their job in proving the concept of lions running in sandals.  The next step would be finding better materials for a reasonable price.