In the process of generating one triple flip, many, many, many, many, many single and double flips will occur and will be caught. That is why ECC is still an effective defense. Attackers don't just get to go straight to their end game.
You can cause any amount of single and double flip without worry. It's not a defence as the attacker can retry till ECC labels it as uncorrectable. AFAIK there is no cost in retrying.
That's true, but none of it is silent. Corrected errors get reported and it will be obvious that something is going wrong to anyone who's paying attention.
Ryzen CPUs report ECC errors like any other modern CPU -- it raises a Machine Check Exception which the operating system is expected to handle. Linux and Windows will both handle and log any ECC errors that the CPU raises. Presumably the various BSDs do as well.
Got a reference? Because my Zen3 desktop has the driver loaded and information shown, just not the bitflips but that may be due to excessively early refresh configuration.
The ECCploit paper has extensive discussion of all the ways their work is detected, and how they even use detection to probe the correction structure. This is not a silent attack. This is a proof that ECC is a penetrable defense. Which we all know! The question is how difficult it is and how stealthily it can be done.
But regardless, ECC still sounds the alarm when it's being attacked. If no one listens, there's not much ECC can do about that.