I just noticed that on longer clips, say more than 5 seconds, there is an increasingly longer pause at the end of the clip. On clips that are say 20 seconds, it is about 1 full second, which completely breaks the continuity of the loop.
The clips are 1280 x 720 Hap codec, I am using an SSD drive, and preloading clips, so I'm not sure what else is possible to improve what seems to be a performance problem.
Also, I am not quantizing clips, though I am using external clock. It doesn't make any difference though whether the clock in external or internal.