Water level in the toilets are not deviating. I can only think of a clog in the lines and they are backfilling and the weak point being the wax rings on the toilets
Call your septic provider,city or whoever. They should have a cleanout at your property line, could be their problem
No I own this one. I am going to try to rent a snake and fix it. It’s starting to back up into the showers now. I had a plumber scheduled to come out tomorrow but after watching YouTube it doesn’t seem to difficult