Just 3 flickering out of large group does not sound like bad ballast, I would rather say one of the LED itself has an open circuit problem (usually bond wire welds on the die get loose, could be due to overheating; high temperature accelerates this type of defects).
The LED life is rather problematic: If you want to prevent the 100/120Hz flicker (many people here are so mad of... :-) ), you have touse an electrolytic capacitor. But once you use an electrolytic capacitor, you have a componentto fail very soon. The problem with higher power lighting is, you have to dissipate a lot of heat. For that you need either a lot of space and large heatsink outside of the fixture (does not look that appealing when OFF), forced air cooling (terrible lifetime of that fan - so practically not usable in general lighting) or operate at higher temperatures (compare to most of the older electronic).
So practically justthe latest approach is the only one usable at this time, but that impose problems the older long life electronic was never faced to: High temperature operation (actually the low operating temperature was assumed as a minimum must when a life longer than few 1000h was needed).
That means many components become not usable anymore, among them the electrolytic and many film capacitors, any package without either being very small or having strain relieve (so using a DFN or QFN for an IC package on
a LED board just can not have different result than it had). But that is often very difficult to explain to many electronic design engineers (IC makers know that, but their customers just foolishly insist on such packages, so at the end the IC makers offer them), when they see such things in their smart phones...
And that means some features are just not possible, when you want reliable light (e.g. being flicker free; although electrolytic capacitor maker's marketing tries to tell otherwise, well just until ask for a 100khour life guarantee)