Does this mean apple is still (never stopped) using TLC or did they go back to it for some reason, like MLC supply issues or something?
As far as I know, all 128GB iPhone 6 models (past, present and future) are TLC and there are really no plans to switch. If anything, I'd expect production to switch to TLC only once reported problems are sorted out, not the opposite way.
For perspective, this is the predicted TLC vs MLC outlook for the next few years; if you think that Apple+Samsung cover 30% of the total NAND market, that means both of them are going to switch to TLC almost exclusively.
Anyway, not all TLC NANDs are bad, most are perfect (at least mine is, never had a single reboot in months).