Not sure if 2018 is the same, I think it may at least be a different part number, dunno for sure.
I have the same issue with my G dam toilet, it is gonna be the death of me. I cant find the dam clog, and the toilet it gonna break my damn floor. I am allergic to paying plumbers, but I have been at it twice cant find it. This is your issue, just like I have a clogged vent, your vent system is why this happens. Does gas pump click off too?