Yes, JB could be very hit-and-miss in concerts. I saw him maybe 7 or 8 times in Los Angeles over the years. That 1979 performance of "La Catedral"? I was sitting right behind Richard Stover, who face-palmed the performance. His sadly wry comment afterward was "That must've been Bream's tribute to all the cathedrals that were bombed out during the War."
In fairness, the players of "that era" generally did NOT focus on nor possess the same technical armory that is common nowadays. I heard Segovia, Yepes, Pepe Romero, Celedonio Romero, Chris Parkening ALL have troubled performances and memory slips of one sort or another. Segovia's late-career glitches are well known, but I heard Pepe come to a dead stop in the middle of a Giuliani piece where he forgot where he was. He rewound to a section beginning and carried through. Yepes dropped out an entire movement of a JSB lute suite. Eliot Fisk played "[Derailed freight train in] Sevilla" once.... It happens. Not so much these days, but it's not that uncommon. We're used to Recorded Perfection in this era, and players who can pretty much deliver this on stage as well.
Salt Lake City, UT