Have you removed the toilets and tried them outside?
If you have one location that plugs in the home, it may be the line.
First try the toilets outside, if it works there, then bring in someone to clear and camera the main line.

: About a month after replacing a chronically ill toilet with a Toto Ultimate, the frequent clogging has again attacked our household. This is only happening to one of the three toilets in the house. A plumber came out just before replacing the toilet and could not find any blockage. I think that it's air in the line, but what do I know, anything ideas on what to do?