From that site.
*8The fundamental flaw in the Pope Joan legend and why any serious historian would reject it is that there is no “gap” in the actual traceable historical record where “Pope Joan” would have served if the legend were true. **
Exactly! Such a made up story that isn’t hard to disprove. And if it were true we are to believe a female Pope was dumb enough to get pregnant, walk around 9 months pregnant and have a baby in public. The things people will believe! Interesting they chose the name Joan— as in of Arc?
There are numerous "gaps" in the so-called unbroken line of popes - even in the one you recently posted. There were even times when two or three popes were all reigning at the same time excommunicating each other and their followers. So, having a gap or not is FAR from a "fundamental flaw".