It does look quite bad at the moment at custom borders and if not sorted very soon it will start to bite.
There was a story of a french lorry driver getting fined for overstaying at a lorry park in Kent whilst he was waiting for his paperwork back. Seems fair to me. He is going to talk to his mates, they aint gonna want to wait for hours or days, and get a fine, and if not sorted out we will end up with shortages.
All that said, this is not a purely brexit problem, it is the crappy government who have implemented it. Yes there were always going to be longer delays at borders, but it is an absoloute shambles. There is no "orderly queue", no strategy for improving things and, as far as I can see, no reall apetite to improve things.
The tories have had 5 years to sort this, and have done absoloutely nothing.
I am flummoxed.