I have had this problem off and on for 2 months. Plumber has been out 3 times, city has inspected their end twice. "No issues." What happens is, the toilets stop draining, and if we run the laundry, the water draining from the washing machine comes up out of the base of the toilets and into the showers.

The plumbers have run a snake, used a camera, the whole bit. No issues all the way to under the street.

The problem goes away by itself for about a week, then hits again. No one has any solutions. Meanwhile I'm without toilets or showers... this time for 2 days and counting.

WOW, if a camera inspection shows no root infiltration nor any cracks, crooked fittings, bellies ,back slope or sags, well that pretty much rules out the probable causes for clogs..

I wonder if you have competent camera people, because SOMETHING is clogged and causing the clog.

My Drain Guy would scope from the roof out to the main and put it all on tape to prove it.

So its not an intermittent vent issue either?

Best Wishes

Describe what you mean by "intermittent vent issue"....how could the vent clog intermittently?